Source : Webster's Revised Unabridged Dictionary (1913)

Palpus \Pal"pus\, n.; pl. {Palpi}. [NL. See {Palp}.] (Zo["o]l.)
   A feeler; especially, one of the jointed sense organs
   attached to the mouth organs of insects, arachnids,
   crustaceans, and annelids; as, the mandibular palpi,
   maxillary palpi, and labial palpi. The palpi of male spiders
   serve as sexual organs. Called also {palp}. See Illust. of
   {Arthrogastra} and {Orthoptera}.