daddy : Idioms & Phrases

• noun long-legged slender flies that resemble large mosquitoes but do not bite
  crane fly.
  
• noun spiderlike arachnid with a small rounded body and very long thin legs
  Phalangium opilio; harvestman.
  

WordNet

Dad"dy long"legs`

Definitions

1. (Zoöl.) 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.
2. (Zoöl.) 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.

Webster 1913

• noun a wealthy older man who gives a young person expensive gifts in return for friendship or intimacy
  

WordNet