The upper (and usually smaller) part (casement) of a window, often hinged a the top / Any glazing above a main window, partition or door / A skylight. / Light from above; toplighting.

(US, idiomatic) Best, or high quality. / (Britain, idiomatic) Describing books, magazines, or movies that have adult content or softcore pornography.

(Canada, ice hockey) The upper part of the goal.

A circus tent, especially the largest in a given circus, where the central attractions take place. / (by extension) The circus; the circus lifestyle.

(idiomatic) The best, or of the highest quality, especially among a range of products.

An item of casual clothing: a top with no sleeves. / The top of a ship's bilge tank, usually the lowest horizontal surface on board.

A one-piece strapless tube-shaped top worn by women, leaving shoulders and belly-button exposed.

(bingo) ninety

(military, government) Information classified at one of the highest levels of sensitivity by a government, based on an assessment that it would cause exceptionally grave damage to national security if disclosed.

A secret that is classed as "top secret"; a top-secret secret; top-secret information. / Used other than figuratively or idiomatically: see top, secret.