a figure of speech combining two contradictory terms

An oxymoron is a figure of speech combining two contradictory terms.

a rhetorical device involving the use of contradiction

An oxymoron is a rhetorical device involving the use of contradiction.

two terms that contradict each other

Oxymoron is two terms that contradict each other, used together.

a Greek term and moros derived from oxy ('sharp') ('dull')

Oxymoron is a Greek term derived from oxy ('sharp') and moros ('dull').