From The Collaborative International Dictionary of English v.0.48 :
nosedive \nose"dive`\, nose-dive \nose"-dive`\v. i.
To drop with the nose or front first, as of an airplane.
Syn: nosedive.
[WordNet 1.5]
From WordNet (r) 3.0 (2006) :
nosedive
n 1: a sudden sharp drop or rapid decline; "the stock took a
nosedive"
2: a steep nose-down descent by an aircraft [syn: dive, nose
dive, nosedive]
v 1: plunge nose first; drop with the nose or front first, of
aircraft