Wordnet 3.0
NOUN (2)
1. 
 a quicker tempo than andante but not as fast as allegro; 
2. 
 a musical composition or musical passage to be performed at a somewhat quicker tempo than andante but not as fast as allegro; 
ADJECTIVE (1)
1. 
 (of tempo) faster than allegro; 
ADVERB (1)
1. 
 in a moderately quick tempo; 
- Example: "play this more allegretto"
The Collaborative International Dictionary of English v.0.48:
Allegretto \Al`le*gret"to\, a. [It., dim. of allegro.] (Mus.)
   Quicker than andante, but not so quick as allegro. -- n. A
   movement in this time.
   [1913 Webster]
WordNet (r) 3.0 (2006):
allegretto
    adv 1: in a moderately quick tempo; "play this more allegretto"
    adj 1: (of tempo) faster than allegro
    n 1: a quicker tempo than andante but not as fast as allegro
    2: a musical composition or musical passage to be performed at a
       somewhat quicker tempo than andante but not as fast as
       allegro