From Proto-West Germanic *laku, from Proto-Germanic *lakō, from Proto-Germanic *lakjaną (“to water, wet, irrigate, drain”), causative of Proto-Germanic *lekaną (“to leak, drain”), from Proto-Indo-European *leǵ- (“to leak”).
Cognate with Old Saxon laca (in placenames, “lake, stream, brook”), Old Norse lækr (“slow flowing stream”), Old English leċċan (“to make wet, moisten”), Old Norse leka (“to drip, leak”). Maybe related to Old High German lacha (“pool, water collected in a ditch, swamp”), Middle Dutch lāke (“pond, lake, stream, brook”), Middle Low German lāke (“water pooled in a riverbed”), which could also be borrowed from lacus (“lake, basin, tank”). More at leak.
- John R. Clark Hall (1916), “lacu”, in A Concise Anglo-Saxon Dictionary, 2nd edition, New York: Macmillan, page 179
- Joseph Bosworth and T. Northcote Toller (1898), “lacu”, in An Anglo-Saxon Dictionary, 2nd edition, Oxford: Oxford University Press.