inclinometer has 2 distinct synonyms spread across 2 of its 3 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.
an instrument showing the angle that an aircraft makes with the horizon
a measuring instrument for measuring the angle of magnetic dip (as from an airplane)
Synonyms, antonyms and the broader and narrower relations for inclinometer come from Princeton University’s WordNet. Full sources and licences.
an instrument used by surveyors in order to measure an angle of inclination or elevation