The Collaborative International Dictionary of English v.0.48:

Philter \Phil"ter\, n. [F. philtre, L. philtrum, Gr. fi`ltron,
   fr. filei^n to love, fi`los dear, loving.]
   A potion or charm intended to excite the passion of love.
   [Written also philtre.] --Addison.
   [1913 Webster]

WordNet (r) 3.0 (2006):

philtre
    n 1: a drink credited with magical power; can make the one who
         takes it love the one who gave it [syn: philter,
         philtre, love-potion, love-philter, love-philtre]