Source : Webster's Revised Unabridged Dictionary (1913)

Lentando \Len*tan"do\ (l[asl]n*t[aum]n"d[-o]; E.
   l[e^]n*t[a^]n"d[-o]), a. [It., p. pr. of lentare to make
   slow. See {Lent}, a.] (Mus.)
   Slackening; retarding. Same as {Rallentando}.