Originally Nautical (later also Aeronautics). Of the wind, etc.: favourable to the course of a ship, aircraft, etc. Also figurative and in…

Of the wind: blowing from a favourable direction. Also (of luck): fortunate, good.

Of a wind: favourable.

Of the wind: blowing in a favourable direction for a ship's course. Frequently in to get (also hold) a good wind. Cf. fair, adj. 7b.

Of weather, climate, a season, a day, etc.: pleasant, fine. Of a wind: favourable for sailing. Also figurative. Obsolete.

That furthers, aids, or helps; helpful. Of a gale: Favourable.

Of a wind: Straight on the line of one's course, favourable. Obsolete.

Of wind or tide: moving in the same direction as the course of a ship, aeroplane, or other object in motion.