Source : Webster's Revised Unabridged Dictionary (1913)

Slumbrous \Slum"brous\, a.
   Slumberous. --Keats.

Source : WordNet®

slumbrous
     adj 1: quiet and tranquil; "a slumberous June morning" [syn: {slumberous}]
     2: inclined to or marked by drowsiness; "slumberous (or
        slumbrous) eyes"; "`slumbery' is archaic"; "the sound had
        a a somnolent effect" [syn: {slumberous}, {slumbery}, {somnolent}]