let has 13 distinct synonyms spread across 6 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 prevent.
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.
actively cause something to happen
“I let it be known that I was not interested”
a brutal terrorist group active in Kashmir; fights against India with the goal of restoring Islamic rule of India
“Lashkar-e-Toiba has committed mass murders of civilian Hindus”
Synonyms, antonyms and the broader and narrower relations for let come from Princeton University’s WordNet. Full sources and licences.