The Collaborative International Dictionary of English v.0.48:

Filibeg \Fil"i*beg\, n. [Gael. feileadhbeag, i. e., little kilt;
   feileadh kilt + beag little, small; cf. filleadh a plait,
   fold.]
   Same as Kilt. [Written also philibeg.]
   [1913 Webster]