luff
noun
°(nautical) The vertical edge of a sail that is closest to the direction of the wind.
"By easing the halyard the luff of the sail sagged to leeward."
verb
°(nautical of a sail) To shake due to being trimmed improperly.
°(nautical of a boat) To alter course to windward so that the sails luff. (Alternatively luff up).