The Collaborative International Dictionary of English v.0.48:

Lento \Len"to\ (l[asl]n"t[-o]; E. l[e^]n"t[-o]), a. & adv. [It.]
   (Mus.)
   Slow; in slow time; slowly; -- rarely written lente.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lento
    adv 1: in music; "Play this lento, please" [syn: lento,
           slowly]
    adj 1: (of tempo) slow