jackstay in Finnish

(nautical) A line (rope, webbing or cable), attached to a boat at the ends, to which a safety harness can be clipped to restrain falling in rough conditions and to prevent falling overboard.

(underwater diving) A line fixed at both ends, which may be used to guide a load or a diver along the route of the line. Uses include guidance to and from the underwater work site, and as a means of controlling an underwater search.