The Collaborative International Dictionary of English v.0.48:
Hydromel \Hy"dro*mel\, n. [L. hydromel, hydromeli, Gr. ?; "y`dwr water + ? honey: cf. F. hydromel.] A liquor consisting of honey diluted in water, and after fermentation called mead. [1913 Webster]WordNet (r) 3.0 (2006):
hydromel n 1: honey diluted in water; becomes mead when fermented