oblique has 5 distinct synonyms spread across 3 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. Its 3 recorded opposites are nominative, parallel, perpendicular.
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.
any grammatical case other than the nominative
Synonyms, antonyms and the broader and narrower relations for oblique come from Princeton University’s WordNet. Full sources and licences.
slanting or inclined in direction or course or position--neither parallel nor perpendicular nor right-angled
“the oblique rays of the winter sun”
indirect in departing from the accepted or proper way; misleading
“used devious means to achieve success”