Yes I have just spotted that Frieze fits absent the U
This comes from 21a An old word for a ball of thread guiding one through a labyrinth or maze, hence the similar word for a hint that points towards the solution of a mystery or puzzle (4) C??? which I took to be CLUE. Is it something else?
Ahh, CLEW not CLUE. The only CLEW I know is the corner of a sail where the leech and foot meet, and in the case of a foresail where the jib or genoa sheets would be attached.