We don't have synonyms for foul wind yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are foul line, fall wind and fore wind.
(n) :
a wind blowing against the direction the sailor wants to go, ie. unfavourably. "Foul" doesn't refer to the strength or character of the wind, only its direction. (Reference: Ray Parkin, H. M. Bark Endeavour, Miegunyah Press, second edition 2003, ISBN 0-522-85093-6, page 210.)
(n) :
a wind blowing against the direction the sailor wants to go, ie. unfavourably. "Foul" doesn't refer to the strength or character of the wind, only its direction. (Reference: Ray Parkin, H. M. Bark Endeavour, Miegunyah Press, second edition 2003, ISBN 0-522-85093-6, page 210.)