Source : Webster's Revised Unabridged Dictionary (1913)

Largo \Lar"go\, a. & adv. [It., large, L. largus, See {Large}.]
   (Mus.)
   Slow or slowly; -- more so than adagio; next in slowness to
   grave, which is also weighty and solemn. -- n. A movement or
   piece in largo time.

Source : WordNet®

largo
     adj : very slow in tempo and broad in manner
     n : (music) a composition or passage that is to be performed in
         a slow and dignified manner
     adv : slowly and broadly