An incomplete U-shaped belt hook, from a sword belt or possibly a horse harness.
A belt hook of similar size and shape, but with a zoomorphic terminal, is illustrated by M J Cuddeford in Identifying Metallic Small Finds (p. 38, No. 55). It is dated 14th to 15th century. Another example is illustrated in Benet’s Artefacts of England & the United Kingdom, M05-0401, where it is described as a ’Sword or Dagger Hanger’. See also UKDFD 770 and UKDFD 33613