Adverse and averse share the root verse, which stems from the Latin term vertere, meaning “to turn.” But their meanings are distinct and, taken literally, antonymic: Adverse, from the Latin word adversus (“turned toward, facing”), means “antagonistic”; the original term conjures of image of confrontation. Averse, meanwhile, comes from aversus (“turned away”) and means “strongly disinclined” or “strongly unfavorable to.”
Other forms of adverse are adversary, meaning “opponent,” and adversity, referring to the quality of opposition. Adversary is also an adjective, but, perhaps because of confusion with the noun form of that word, adversarial came to prevail in that usage. Avert, meanwhile, is related to averse and means “to turn away, to avoid.” (Veer, though it has the same meaning, is unrelated; it’s from a Germanic word meaning “to slacken.”)
A whole family of other words with the verse root exist: Converse means “the exact opposite” and has the noun and verb form convert, meaning “someone who turns” and “to turn,” respectively, and the noun form conversion, referring to the act of converting. Converse also means “to speak with someone” (to “turn” speech) and leads to the adjective conversant and the noun conversation. (The latter used to also mean “living together” or “having sexual relations.”) Diverse, originally divers, means “distinct” and is the parent of diversity, divergent, divert, and diversion.
Extrovert, which means “turned outward,” is mirrored by the antonym introvert. (These also serve as noun forms.) Inverse means “turn about” or “turn over” and has the verb form invert and the noun form inversion. Obverse, meaning “turned toward,” is the opposite of reverse, “turned away,” which, unlike the more rarely used obverse, has a noun form, too: reversal. Perverse, which means “turned away (from what is correct),” has the noun forms pervert, for a person, and perversion, for the quality. Transverse means “turned across” (the rare noun form is transversal), and traverse means “to pass across.”
Versus also ultimately derives from vertere by way of, well, versus. (The Old English suffix -weard, from which we derive -ward — seen in toward, forward, and so on — is akin to versus.) Other related words include verse (from the idea of “turning” from one line of verse to another), versed (“knowledgeable” — literally, “one who knows verses,” with the connotation of one who “turns over” a subject of study), and versify, or “write verse.”
Anniversary, meanwhile, literally means “year turning,” and universe, originally meaning “all together,” is derived from the words for “one” and “turn.” University, referring to a place of learning, stems from the idea of “whole,” with the connotation of “community.” (Varsity, an alteration of a shortening of university, denotes the primary group of athletes in any sport who represent a university or other school.)