Source : Webster's Revised Unabridged Dictionary (1913)

Whilom \Whi"lom\ (hw[imac]"l[u^]m), adv. [AS. hw[=i]lum,
   properly, at times, dative pl. of hw[=i]l; akin to G. weiland
   formerly, OHG. hw[=i]l[=o]m, See {While}, n.]
   Formerly; once; of old; erewhile; at times. [Obs. or Poetic]
   --Spenser.

         Whilom, as olde stories tellen us, There was a duke
         that highte Theseus.                     --Chaucer.