If something is forgettable, it is not bad enough to hate and not good enough to stay with you — a film, a meal, a pop song, a person you met once at a party. The word is often a little dry and a little funny: calling a book perfectly forgettable is a polite way to say it was dull. People use it more as a quiet put-down than as a neutral fact. The opposite, unforgettable, is the common praise-word; forgettable is its smiling twin, and you hear that humour in it. It is about the thing failing to stick, not about a person who loses keys.