pain has 15 distinct synonyms spread across 7 of its 7 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 pleasure.
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.
a symptom of some physical hurt or disorder
“the patient developed severe pain and distension”
emotional distress; a fundamental feeling that people try to avoid
“the pain of loneliness”
a somatic sensation of acute discomfort
“as the intensity increased the sensation changed from tickle to pain”
a bothersome annoying person
“that kid is a terrible pain”
something or someone that causes trouble; a source of unhappiness
“washing dishes was a nuisance before we got a dish washer”
cause emotional anguish or make miserable
“It pains me to see my children not being taught well in school”
Synonyms, antonyms and the broader and narrower relations for pain come from Princeton University’s WordNet. Full sources and licences.