n. & v. Naut.
n. each of several strips across a sail, for taking it in or rolling it up to reduce the surface area in a high wind.
v.tr. 1 take in a reef or reefs of (a sail). 2 shorten (a topmast or a bowsprit). reefing-jacket a thick close-fitting double-breasted jacket. reef-knot a double knot made symmetrically to hold securely and cast off easily. reef-point each of several short pieces of rope attached to a sail to secure it when reefed.
[ ME riff, refe f. Du. reef, rif f. ON rif RIB, in the same sense: cf. REEF(1) ]