NOUN (1)

1. a gradually increasing tempo of music;
- Example: "my ear will not accept such violent accelerandos"


ADJECTIVE (1)

1. gradually increasing in tempo;


ADVERB (1)

1. with increasing speed;
- Example: "here you must play accelerando"

The Collaborative International Dictionary of English v.0.48:

Accelerando \Ac*cel`er*an"do\, a. [It.] (Mus.)
   Gradually accelerating the movement.
   [1913 Webster]

WordNet (r) 3.0 (2006):

accelerando
    adv 1: with increasing speed; "here you must play accelerando"
    adj 1: gradually increasing in tempo
    n 1: a gradually increasing tempo of music; "my ear will not
         accept such violent accelerandos"