Source : Webster's Revised Unabridged Dictionary (1913)

Nit \Nit\, n. [AS. hnitu; akin to D. neet, G. niss, OHG. niz;
   cf. gr. ?, ?, Icel. gnit, Sw. gnet, Dan. gnid, Russ. & Pol.
   gnida, Bohem. hnida, W. nedd.] (Zo["o]l.)
   The egg of a louse or other small insect.

   {Nit grass} (Bot.), a pretty annual European grass
      ({Gastridium lendigerum}), with small spikelets somewhat
      resembling a nit. It is also found in California and
      Chili.

Source : WordNet®

nit
     n 1: a luminance unit equal to 1 candle per square meter measured
          perpendicular to the rays from the source
     2: egg or young of an insect parasitic on mammals especially a
        sucking louse; often attached to a hair or item of
        clothing