The Collaborative International Dictionary of English v.0.48:

February \Feb"ru*a*ry\, n. [L. Februarius, orig., the month of
   expiation, because on the fifteenth of this month the great
   feast of expiation and purification was held, fr. februa,
   pl., the Roman festival or purification; akin to februare to
   purify, expiate.]
   The second month in the year, said to have been introduced
   into the Roman calendar by Numa. In common years this month
   contains twenty-eight days; in the bissextile, or leap year,
   it has twenty-nine days.
   [1913 Webster]

WordNet (r) 3.0 (2006):

February
    n 1: the month following January and preceding March [syn:
         February, Feb]