The Collaborative International Dictionary of English v.0.48:

Alcaid \Al*caid"\, Alcayde \Al*cayde"\, n. [Sp. alcaide, fr. Ar.
   al-q[=a][imac]d governor, fr. q[=a]da to lead, govern.]
   1. A commander of a castle or fortress among the Spaniards,
      Portuguese, and Moors.
      [1913 Webster]

   2. The warden, or keeper of a jail.
      [1913 Webster]