Adversary

The noun (and occasional adjective) adversary (~ 'opponent', 'enemy') has different pronunciations in American and British English.

• In traditional British RP, the pronunciation you are most likely to hear in academic circles in the UK, the stress is on the first syllable, and the two central vowels are all variants of the loose shwa (the second sometimes assimilated): 'AD-verse-er-y', IPA: /'æd və^r s^ə rɪ/
• The GA pronunciation stresses the second syllable, which has the stronger vowel sound of 'heard': 'ad-VERSE-er-y', /æd 'vɜː sə rɪ/. This pronunciation appears to be gaining acceptance in colloquial British English.
• Note that the related adjective adversarial has the stress on the third syllable - IPA: / ,æd vɜː 'sɛə rɪəl/.

You may also like to see AWE's advice on adverse and averse.