Complementary pairs of antonyms are perfect opposites without a continuum of intermediate states in between. Dead is the complementary antonym of alive. Inhale is the complementary antonym of exhale.
Gradable pairs of antonyms are opposites at the extreme ends of a continuum of states. The word first is the gradable antonym of last. Second, third and fourth are examples of words on the continuum in between.
Relational opposite antonyms are words with opposite meanings that are used in similar circumstances. Teach is the relational opposite of learn. Predator is the relational opposite of prey.
Sometimes words are relational opposites only within a particular context. In a Cold War mentality, Russian is the antonym of American. Outside of a Cold War mentality, this is not necessarily the case.
The words adhere and separate have a unique characteristic: they are both synonyms of the word cleave, yet they are antonyms of each other.