indication has 4 distinct synonyms spread across 3 of its 5 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 contraindication.
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.
something that serves to indicate or suggest
“an indication of foul play”
Synonyms, antonyms and the broader and narrower relations for indication come from Princeton University’s WordNet. Full sources and licences.
(medicine) a reason to prescribe a drug or perform a procedure
“the presence of bacterial infection was an indication for the use of antibiotics”
something (as a course of action) that is indicated as expedient or necessary
“there were indications that it was time to leave”
a datum about some physical state that is presented to a user by a meter or similar instrument
“he could not believe the meter reading”