The Collaborative International Dictionary of English v.0.48:

Legato \Le*ga"to\ (l[asl]*g[aum]"t[-o]), a. [It., tied, joined,
   fr. legare to tie, bind, L. ligare.] (Mus.)
   Connected; tied; -- a term used when successive tones are to
   be produced in a closely connected, smoothly gliding manner.
   It is often indicated by a tie, thus ?, ?, or ?, ?, written
   over or under the notes to be so performed; -- opposed to
   staccato.
   [1913 Webster]

WordNet (r) 3.0 (2006):

legato
    adv 1: connecting the notes; in music; "play this legato,
           please" [ant: staccato]
    adj 1: (music) without breaks between notes; smooth and
           connected; "a legato passage" [syn: legato, smooth]
           [ant: disconnected, staccato]