Source : Webster's Revised Unabridged Dictionary (1913)

Hydromel \Hy"dro*mel\, n. [L. hydromel, hydromeli, Gr. ?; ?
   water + ? honey: cf. F. hydromel.]
   A liquor consisting of honey diluted in water, and after
   fermentation called mead.

Source : WordNet®

hydromel
     n : honey diluted in water; becomes mead when fermented