IPA: /ˌæntɪˈθɛtɪk/
KK: /æn'tɪθɛtɪk/
Describing something that is directly opposed or contrasting to something else.
The two theories are antithetic, representing completely different viewpoints on the issue.
Antithetic → It is formed from "anti-" (meaning against) and "tithenai" (Greek for to place or set). The word describes something that is set against or in opposition to something else.
Think of 'against' ('anti-') and 'placing' ('tithenai') to remember that 'antithetic' refers to ideas or things that are in opposition to each other.