burdened has 2 distinct synonyms spread across 1 of its 2 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 unburdened.
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.
bearing a heavy burden of work or difficulties or responsibilities
“she always felt burdened by the load of paper work”
bearing a physically heavy weight or load
“tree limbs burdened with ice”
Synonyms, antonyms and the broader and narrower relations for burdened come from Princeton University’s WordNet. Full sources and licences.