The Collaborative International Dictionary of English v.0.48:
Luff \Luff\ (l[u^]f), v. i. [imp. & p. p. Luffed (l[u^]ft); p.
pr. & vb. n. Luffing.]
1. (Naut.) To turn the head of a vessel toward the wind; to
sail nearer the wind; to turn the tiller so as to make the
vessel sail nearer the wind.
2. (Naut.) To flutter or shake from being aligned close to
the direction of the wind; -- said of a sail.
To luff round, or To luff alee, to make the extreme of
this movement, for the purpose of throwing the ship's head
into the wind.