'Hair grass' definitions:

Definition of 'hair grass'

(from WordNet)
noun
Fine-leaved aquatic spike rush; popular as aerator for aquariums [syn: needle spike rush, needle rush, slender spike rush, hair grass, Eleocharis acicularis]

Definition of 'Hair grass'

From: GCIDE
  • Hair grass \Hair" grass`\ (gr[.a]s`). (Bot.) A grass with very slender leaves or branches; as the Agrostis scabra, and several species of Aira or Deschampsia. [1913 Webster]