minor has 19 distinct synonyms spread across 4 of its 12 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 major.
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.
of lesser importance or stature or rank
“a minor poet”
lesser in scope or effect
“had minor differences”
inferior in number or size or amount
“a minor share of the profits”
(of a scale or mode) having half steps between the second and third degrees, and (usually) the fifth and sixth degrees, and the seventh and eighth degrees
“the minor keys”
of lesser seriousness or danger
“suffered only minor injuries”
of your secondary field of academic concentration or specialization
relatively moderate, limited, or small
“a small business”
have as one's secondary field of study
“in collee she minored in mathematics”
1 of the 12 recorded senses carries no synonym, antonym or related term, so it is not shown above. Every sense, with its definition and examples, is on the full entry for minor.
Synonyms, antonyms and the broader and narrower relations for minor come from Princeton University’s WordNet. Full sources and licences.