plumb rule

1. 1.

   a plumb line attached to a narrow board

   Broaderplumb line

Questions about plumb rule

What does plumb rule mean?

plumb rule means "a plumb line attached to a narrow board".

Is plumb rule a common word?

plumb rule is banded "Rare" — specialist or archaic — most readers will not have met it. The band comes from how often the word appears in a large corpus of everyday English, not from an editor's impression.