Longman Dictionary of Contemporary English - nosedive

~1 n 1 a sudden drop in amount, price, rate etc  (The pound took a nosedive on the foreign exchange market today.) 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.) ~2 v 1 if a price, rate, amount etc nosedives, it becomes smaller or reduces in value suddenly 2 if a plane nosedives, it drops suddenly and steeply with its front end pointing towards the ground