In the chemical sense, 'water hating'. Just as oil and water don't mix, so hydrophobic chemicals tend not to dissolve very well in water. Indeed, many organic dyes and perfumes need to be extracted by using oils and fats which provide suitable solvation. For special cases, like french dressing or paint (or milk), an emulsion is needed where the emulsifying agent (eg mustard in dressing) makes small micelles of the fatty components which disperse in the water. This is what makes milk white.

Hy`dro*phob"ic (?), a. [L. hydrophobicus, Gr. : cf. F. hydrophobique.]

Of or pertaining to hydrophobia; producing or caused by rabies; as, hydrophobic symptoms; the hydrophobic poison.

© Webster 1913.