Noun
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.
Source: Webster's dictionary