conditions has 3 distinct synonyms spread across 1 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.
the prevailing context that influences the performance or the outcome of a process
“there were wide variations in the conditions of observation”
the set of circumstances that affect someone's welfare
“hazardous working conditions”
the atmospheric conditions that comprise the state of the atmosphere in terms of temperature and wind and clouds and precipitation
“they were hoping for good weather”
Synonyms, antonyms and the broader and narrower relations for conditions come from Princeton University’s WordNet. Full sources and licences.