forelock (n.)

"lock of hair growing above the forehead," Old English forelocca "forelock;" see fore- + lock (n.2).

"Opportunity has hair in front, behind she is bald; if you seize her by the forelock, you may hold her; but, if she once escapes, not Jupiter himself can catch her again." ["Dictionary of Latin Quotations, Proverbs, Maxims and Mottos," H.T. Riley, London, 1866]