An example of someone who is the antithesis of friendly is a grump.
Hope is the antithesis of despair.
Joy is the antithesis of sorrow.
Origin of antithesis
- Late Latin from Greek from antitithenai antithe- to oppose anti- anti- tithenai to set dhē- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition
- From Ancient Greek ἀντί (anti, “against”) + θέσις (thesis, “position”).