Purlin is a support board of a roof.
An example of a purlin is a horizontal wooden board holding up the rafters of a roof.
One of several horizontal timbers supporting the rafters of a roof.
A horizontal timber supporting the rafters of a roof.
Origin of purlin
Information on the origin of the term is scant at best. According to Websters it comes from the 15th century English. According to the Oxford Concise Dictionary, it is "Middle English, perhaps of French origin". All other sources referenced Middle English or 15th Century English.