Undercommon: The Language of the Underdark in 5e

Welcome to our guide to Undercommon — the shared language of cultures who dwell in the fearsome Underdark and one of Dungeons & Dragons 5e’s 16 languages found in the Player’s Handbook. We’re going to go over who speaks undercommon, its origins, some words that are derived from it, and why it has nothing to do with being able to speak common. 

Where Do They Speak Undercommon? 

Deep below the sunlit world, through caverns black and sodden overgrown with towering zurkhwood fungi the size of trees lies the underdark. It is a cruel and perilous place — a vast network of subterranean passageways, lakes, tunnels, and caves that are rumored to go on forever. 

Get lost in the underdark, and you should count yourself lucky if you’re eaten by the giant spiders or a gelatinous cube before something worse finds you. This shadowy realm is populated by some of the most dangerous creatures in all of Dungeons & Dragons, from the sadistic Drow and Duergar to the nightmarish mind flayers themselves. 

However, just because you’re a dark elf slaver whose whole thing is dressing like you were dragged backward through a fetish convention on your way home from the bulk discount knife shop, doesn’t mean you can just murder-enslave everything you come across. Someone has to buy all these enslaved adventurers, for one thing. Sooner or later you’re going to need to figure out how to talk to someone who isn’t another Drow. 

Who Speaks Undercommon? 

Much like common evolved on the surface world as a way for humans, elves, dwarves, and other lineages to communicate, undercommon is the shared language of the various intelligent species that populate the Underdark.

Duergar (the deep dwarves), Svirfneblin (deep gnomes), Drow (dark elves), and virtually all other intelligent life down in the Underdark all use undercommon as a collective second language through which they communicate. 

Even intelligent aberrations like Mind Flayers (“Illithid” is actually an undercommon word) and Beholders will be able to speak undercommon — although aberrations have their own shared tongue known as Deep Speech.  

There are 80 entries in the Monster Manual and Monsters of the Multiverse that speak or understand undercommon. Basically, if you find yourself walking through a cave that goes down for a few days and you run into anyone who looks like they belong there, they probably speak undercommon. 

Undercommon vs. Common: What Does Undercommon Sound Like? 

Interestingly, it’s unclear whether common was originally a prevalent human language that became the Forgotten Realms’ lingua franca, or whether it was a shared trading language that was adopted by humans, making it technically a kind of creole (as it has native speakers). 

Therefore, no one really knows (i.e., it’s up to the GM) what common sounds like, but it’s assumed to be whatever language you’re playing the game in. 

It’s actually a little easier to trace undercommon back to its roots because there aren’t any large human cultures native to the Underdark. This means that — as noted in the Player’s Handbook — undercommon is a shared second language created for use by Underdark traders. Therefore, it probably has a bit of elvish, dwarvish, gnomish, and a few other darker phrases borrowed from forgotten corners of the Underdark. 

Elvish is probably the dominant element of undercommon, just as drow are the dominant sentient culture throughout most of the Underdark. We can tell this because the written script used for undercommon is elvish in origin. 

A character who speaks elvish (or another elvish-derived language like Sylvan) might hear an uncanny mixture of words and sentence structures that they half recognize and understand when they listen to someone speaking undercommon — like a German speaker can grasp a fair amount of what’s being said by someone speaking Dutch or Afrikaans. 

Therefore, I would rule that there’s a chance anyone who shares a language with one of the main contributory languages that make up undercommon (dwarvish, gnomish, and elvish) could make an Intelligence check (start at DC20, and reduce it by 2 for every related language known as well as another 1 per number of times the PC has interacted with someone who speaks undercommon), and it can be made once per NPC interaction to grasp the gist of the conversation. 

I would also rule that a character trying to learn undercommon would have the time required reduced by knowing languages related to it — but I play D&D with a bunch of bi- and tri-lingual people, which means that not only do all the elves in my game speak Spanish, but I spend way more time thinking about how languages relate to one another than I probably need to or should.  

What undercommon almost certainly has nothing in common with is the common language. 

They’ve both developed largely separately from one another over thousands of years and rarely come into contact. The fact their names are so similar is a bit of a false friend, and if you’re being true to the lore of D&D 5e, undercommon will sound completely different from common, despite the implication that they’re derivations of the same original form of communication. 

Should I Learn Undercommon? 

Like most languages, whether or not your character does or doesn’t know how to speak them is dependent on your backstory. This is especially true of the exotic languages as it’s very unlikely your character would have had a chance to pick one of them up outside of studying them in an academic sense or having a close personal relationship with someone who spoke a particular language. 

Picking up conversational dwarvish, on the other hand, is probably akin to native English speakers in the United States all knowing at least a little Spanish through exposure (French being the slightly rarer stand-in for elvish here, which I guess makes undercommon kind of similar to Quebecois? But that’s not important). 

If your next PC has spent time in the Underdark (probably as an involuntary permanent labor volunteer of the Drow) or was originally from below, they almost certainly speak undercommon. Also, if you want your various languages to be as useful as possible, I would skip undercommon unless you’re certain you’re headed for the Underdark. 

Undercommon Phrases 

There are a number of common monster names and other scraps of D&D terminology which are derived from undercommon, including… 

  • Abster: “memory”
  • Al: “dead, death”
  • Arint: “gourmet of, taster”
  • Ator: “elder, revered”
  • Bossk: “lord, master”
  • Corian: “leader, liaison”
  • Hion: “black, dark, darkness”
  • Hoon: “abomination, outsider”
  • Illi: “mind”
  • Ilsen: “brain”
  • Lugri: “fear, feared”
  • Maanze: “creed, law”
  • Malin: “arcane, psionic”
  • Mious: “sage, scholar”
  • Ordell: “golem, humanoid, mind flayer”
  • Quas: “honor”
  • Sine: “great, powerful”
  • Tharid: “devour, devourer”
  • Thelid: “conqueror, eater”
  • Thid: “flayer, ruler”
  • Tor: “elder, revered” 
  • Uli: “noble”
  • Ullip: “thought”
  • Urop: “servant, slave, thrall”
  • Xalli: “disgust, pain”
  • Zin-carla: “Spirit-wraith”