opinio

Opinio, opinionis is third declension feminine, from opinor, "suppose". Note the single p: the English opinion doubles nothing, but plenty of learners write oppinio by analogy with oppono.

Three senses, and the second and third catch people out. Straightforwardly it is a belief or judgement, close to sententia. But opinio also means the belief other people hold about you, so magna opinio is a good reputation, and opinione celerius means "faster than expected", an ablative of comparison against what was believed. Latin does not share the English snobbery about the word: for Cicero opinio is what you hold short of certain knowledge, which is a real epistemological claim rather than a put-down.