'Prestissimo' definitions:

Definition of 'prestissimo'

From: WordNet
adverb
Extremely fast; as fast as possible; "this passage should be played prestissimo"
adjective
(of tempo) as fast as possible

Definition of 'Prestissimo'

From: GCIDE
  • Prestissimo \Pres*tis"si*mo\, adv. [It., superl. of presto.] (Mus.) Very quickly; with great rapidity. [1913 Webster]