The Collaborative International Dictionary of English v.0.48:

Najadaceae \Najadaceae\ prop. n.
   A monotypic family of aquatic plants having narrow leaves and
   small flowers; same as Naiadaceae; the naiad family.

   Syn: Naiadaceae, family Naiadaceae, family Najadaceae,
        naiad family.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

Najadaceae
    n 1: monotypic family of aquatic plants having narrow leaves and
         small flowers [syn: Naiadaceae, family Naiadaceae,
         Najadaceae, family Najadaceae, naiad family]