ADJECTIVE (1)

1. (of tempo) as fast as possible;


ADVERB (1)

1. extremely fast; as fast as possible;
- Example: "this passage should be played prestissimo"

The Collaborative International Dictionary of English v.0.48:

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

WordNet (r) 3.0 (2006):

prestissimo
    adv 1: extremely fast; as fast as possible; "this passage should
           be played prestissimo"
    adj 1: (of tempo) as fast as possible