Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
FLASH
As described in historical dictionaries
Patronymica Britannica (1860)
FLASH. See under Flashnian. The Prompt. Parv. defines flasshe as ' watyr,' and under -'ff' 7(6' we have " llasche, where rayne watyr stondythe." ilr. '\'ay says, "a shallow jdooI, in low Latin flacltin, jiasca, 0. Yy. facile ov Jfesqie." Camden, in his Britannia, applies the term to those artificial reservoirs in Sussex which had been formed for the driving of ironmills.