I. nose‧dive¹ /ˈnəʊzdaɪv $ ˈnoʊz-/ noun [countable]

1. a sudden very large fall in the price, value, or condition of something:
The pound took a nosedive on the foreign exchange market today.
The economy went into a nosedive.

2. a sudden steep drop made by a plane with its front end pointing towards the ground:
Everyone screamed as the plane suddenly went into a nosedive.

[TahlilGaran] Dictionary of Contemporary English ▲

II. nosedive² verb [intransitive]

1. if a price, value, or condition of something nosedives, it suddenly goes down or gets much worse Synonym : plummet:
Sales have nosedived since January.

2. if a plane nosedives, it drops suddenly and steeply with its front end pointing towards the ground

[TahlilGaran] Dictionary of Contemporary English ▲