wythe
A continuous vertical section of masonry, one unit in thickness.
That wall has to be at least three wythes of brick to support your load.
A partition between flues in a chimney.
A chimney runs from the base of the first flue liner to the top of the last flue liner, or to any rain cap above it. Attach single-wythe chimneys to the house.
Where it comes from
Uncertain. * Perhaps an alteration of width. * Perhaps related to withe (“flexible twig; band of twigs”), from Old English wiþþe (“tie, band”). The chimney-partition sense may derive from the fact that a single wythe or thickness of brick has often been used for such partitions.
Adapted from the Wiktionary entry wythe (CC BY-SA 4.0).