[ 'α:kɪtreɪv ]
■ noun
1》 (in classical architecture) a main beam resting across the tops of columns.
2》 the frame around a doorway or window.
↘a moulding round the exterior of an arch.
Origin
C16: from Fr., from Ital., from archi- 'chief' + -trave from L. trabs , trab- 'a beam'.