Nose-dive

[nohz-dahyv] /ˈnoʊzˌdaɪv/

noun, Also, nose dive
1.
a plunge of an aircraft with the forward part pointing downward.
2.
a sudden sharp drop or rapid decline:
a time when market values were in a nosedive.
verb (used without object), nosedived or nosedove, nosedived, nosediving. Also, nose-dive
3.
to go into a nosedive:
a warning that prices might nosedive.
n.

“sudden large decrease,” 1920, from airplane sense, first attested 1912, from nose (n.) + dive (n.). As a verb from 1915.