yard arm, n.

1. Nautical Slang The part of a boat which, wherever the observer is, the sun is just past. i.e. "The sun is well past the yard arm - it must be time for a gin and tonic!". See also yard, arm

Yard"arm` (?), n. Naut.

Either half of a square-rigged vessel's yard, from the center or mast to the end.

⇒ Ships are said to be yardarm and yardarm when so near as to touch, or interlock yards.

© Webster 1913.