attitude has 3 distinct synonyms spread across 2 of its 4 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a complex mental state involving beliefs and feelings and values and dispositions to act in certain ways
“he had the attitude that work was fun”
the arrangement of the body and its limbs
“he assumed an attitude of surrender”
a theatrical pose created for effect
“the actor struck just the right attitude”
position of aircraft or spacecraft relative to a frame of reference (the horizon or direction of motion)
Synonyms, antonyms and the broader and narrower relations for attitude come from Princeton University’s WordNet. Full sources and licences.