luff

/lสŒf/
noun
  1. 1

    The vertical edge of a sail that is closest to the direction of the wind.

    โ€œBy easing the halyard, the luff of the sail was made to sag to leeward.โ€

  2. 2

    The act of sailing a ship close to the wind.

  3. 3

    The roundest part of a ship's bow.

  4. 4

    The forward or weather leech of a sail, especially of the jib, spanker, and other fore-and-aft sails.

verb
  1. 1

    (of a sail) To shake due to being trimmed improperly.

  2. 2

    (of a boat) To alter course to windward so that the sails luff. (Alternatively luff up)

  3. 3

    To let out (a sail) so that it luffs.

  4. 4

    To alter the vertical angle of the jib of a crane so as to bring it level with the load.

Source: https://en.wiktionary.org/wiki/luff