unskilled has 4 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. Its one recorded opposite is skilled.
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.
not having or showing or requiring special skill or proficiency
“unskilled in the art of rhetoric”
not doing a good job
“incompetent at chess”
Synonyms, antonyms and the broader and narrower relations for unskilled come from Princeton University’s WordNet. Full sources and licences.