antithetical

Concise Oxford English Dictionary © 2008 Oxford University Press:
antithetical /ˌantɪˈθɛtɪk(ə)l/

▶adjective

• 1 mutually incompatible.

• 2 relating to or using the rhetorical device of antithesis.

– derivatives
antithetic adjective,
antithetically adverb.

– origin C16: from Gk antithetikos, from antithetos ‘placed in opposition’.