Source : Webster's Revised Unabridged Dictionary (1913)

Mastoidal \Mas*toid"al\, a.
   Same as {Mastoid}.

Source : WordNet®

mastoidal
     adj 1: of or relating to or in the region of the mastoid process
     2: relating to or resembling a nipple [syn: {mastoid}]

mastoidal
     n : process of the temporal bone behind the ear at the base of
         the skull [syn: {mastoid}, {mastoid process}, {mastoid
         bone}]