inclination has 13 distinct synonyms spread across 7 of its 8 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. Its one recorded opposite is disinclination.
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.
an attitude of mind especially one that favors one alternative over others
“he had an inclination to give up too easily”
(astronomy) the angle between the plane of the orbit and the plane of the ecliptic stated in degrees
(geometry) the angle formed by the x-axis and a given line (measured counterclockwise from the positive half of the x-axis)
(physics) the angle that a magnetic needle makes with the plane of the horizon
that toward which you are inclined to feel a liking
“her inclination is for classical music”
a characteristic likelihood of or natural disposition toward a certain condition or character or effect
“the alkaline inclination of the local waters”
Synonyms, antonyms and the broader and narrower relations for inclination come from Princeton University’s WordNet. Full sources and licences.