The Collaborative International Dictionary of English v.0.48:

Phalangoidea \Phal`an*goi"de*a\, n. pl. [NL., from Phalangium
   the daddy longlegs (see Phalangious) + Gr. e'i^dos form.]
   (Zool.)
   A division of Arachnoidea, including the daddy longlegs or
   harvestman (Phalangium) and many similar kinds. They have
   long, slender, many-jointed legs; usually a rounded,
   segmented abdomen; and chelate jaws. They breathe by
   trache[ae]. Called also Phalangides, Phalangidea,
   Phalangiida, and Opilionea.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Daddy longlegs \Dad"dy long"legs`\
   1. (Zool.) An arachnidan of the genus Phalangium, and
      allied genera, having a small body and four pairs of long
      legs; -- called also harvestman, carter, and
      grandfather longlegs.
      [1913 Webster]

   2. (Zool.) A name applied to many species of dipterous
      insects of the genus Tipula, and allied genera, with
      slender bodies, and very long, slender legs; the crane
      fly; -- called also father longlegs.
      [1913 Webster]

WordNet (r) 3.0 (2006):

daddy longlegs
    n 1: long-legged slender flies that resemble large mosquitoes
         but do not bite [syn: crane fly, daddy longlegs]
    2: spiderlike arachnid with a small rounded body and very long
       thin legs [syn: harvestman, daddy longlegs, Phalangium
       opilio]

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "daddy longlegs":
   arachnid, arthropod, beetle, bug, caterpillar, centipede, chilopod,
   diplopod, fly, harvestman, hexapod, insect, larva, maggot,
   millepede, millipede, mite, nymph, scorpion, spider, tarantula,
   tick