to plunge into water headfirst, with arms extended forward

to swim underwater using breathing equipment

said of a submarine: to submerge

said of a bird or an aircraft: to descend steeply through the air

said of prices or profits: to plummet

(+ into) to plunge one's hand into (a container, etc)

She dived into her shopping bag and brought out a crumpled receipt

(+ into) to plunge into (some activity)

He dived eagerly into his work

(+ for) to dash for (cover or shelter)

to lunge

He dived at her and she sidestepped

a headlong plunge into water, e.g. one performed with prescribed moves in competitive diving

the submerging of a submarine

a steep descent by an aircraft

a sharp decline

a steep dive in profits

informal a disreputable bar or meeting place

a ploy in football in which a player falls over deliberately and ostentatiously after being tackled in order to give the effect of having been fouled