adversarial

UK: /ˌædvə^rˈsɛəriəl/ US: /ˌædvɚˈsɛriəl/

Collins Concise English Dictionary © HarperCollins Publishers::

adversarial / ˌædvɜːˈsɛərɪəl/ adjective

1. pertaining to or characterized by antagonism and conflict

WordReference Random House Learner's Dictionary of American English © 2025

ad•ver•sar•y /ˈædvɚˌsɛri/   n., pl. -ies. [countable]

1. a person, group, etc., that opposes or attacks; opponent;
   enemy:
   She was a dangerous political adversary.

ad•ver•sar•i•al /ˌædvɚˈsɛriəl/  adj. See -vert-.

WordReference Random House Unabridged Dictionary of American English © 2025

ad•ver•sar•y  (ad′vər ser′ē), n., pl. -sar•ies, adj. 
n. 

1. a person, group, or force that opposes or attacks; opponent;
   enemy;
   foe.
2. a person, group, etc., that is an opponent in a contest;
   contestant.
3. the Adversary, the devil;
   Satan.

adj. Also,[esp. Brit.,] ad•ver•sar•i•al 

(ad′vər•sâr′ē•əl). 
4. of or pertaining to an adversary.
5. involving adversaries, as plaintiff and defendant in a legal proceeding:
   an adversary trial.

• Anglo-French
• Latin adversārius, equivalent. to advers(us) (see adverse) + -ārius -ary; replacing Middle English adversere
• Middle English adversarie 1300–50

ad′ver•sar′i•ness, n. 
Synonyms

• 1. Adversary, antagonist mean a person or a group contending against another.
  Adversary suggests an enemy who fights determinedly, continuously, and relentlessly:
  a formidable adversary.
  Antagonist suggests one who, in hostile spirit, opposes another, often in a particular contest or struggle:
  a duel with an antagonist.

Antonyms

• 1. ally.