fear has 10 distinct synonyms spread across 5 of its 8 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 fearlessness.
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.
be afraid or feel anxious or apprehensive about a possible or probable situation or event
“I fear she might get aggressive”
be sorry; used to introduce an unpleasant statement
“I fear I won't make it to your wedding party”
an emotion experienced in anticipation of some specific pain or danger (usually accompanied by a desire to flee or fight)
a feeling of profound respect for someone or something
“the fear of God”
1 of the 8 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 fear.
Synonyms, antonyms and the broader and narrower relations for fear come from Princeton University’s WordNet. Full sources and licences.