The Collaborative International Dictionary
Femerell
Femerell \Fem"er*ell\, n. [OF. fumeraille part of a chimney. See Fume.] (Arch.) A lantern, or louver covering, placed on a roof, for ventilation or escape of smoke.
Wiktionary
femerell
n. (context archaic English) The lantern, louvre, or covering placed in the ridge of a hall roof for the purpose of ventilation or letting out the smoke of the fire kindled on a central hearth.