Origin of the word "lake"

The word lake has a complicated and, in part, an uncertain history due to a merging of inherited Middle English lake, ("small stream of running water, pool, lake"), with Middle English lac ("lake"), which comes from Old French lac ("lake") or Latin lacus ("lake, pond, basin, reservoir").

The Middle English lake ("stream, pool, lake") is related to Dutch laak ("stream, drainage ditch, pond"), Low German Lake, Laak ("drainage, marshland"), German Lache ("puddle, pool"), Icelandic lækur ("stream"), and comes from the original reconstructed Proto-Indo-European root word *leg-, which means ("to leak"). The descendants of this word follow more than one lineage. However, below shows the progression through the Germanic/English lineage. Words in bold shows the merging period:
 * Proto-Germanic *lakō → leak, drain, puddle, pool, lake (+ others)
 * Proto-West Germanic *laku → stream, pool or lake
 * Old English: lacu → pool, pond, expanse of water, or lake
 * Middle English: lāke, lac → expanse of water, lake, pond, pool, reservoir (+ others)
 * English: lake → a large, landlocked stretch of water or similar liquid

From the original reconstructed Proto-Indo-European root word lókus, which means ("pond, pool"), the descendants of this word follow the progression through the Italic/French lineage:
 * Proto-Italic lakus → lake
 * Latin lacus → lake, pond, basin, reservoir
 * Old French lai → pond, lake (displaced)
 * Old French lac? → lake
 * Middle French lac → lake
 * French lac → lake
 * Norman lac → lake (from )

The displacement of Old French lai could have been assisted by influence from the early Middle English words lac, lace, and the Old English word lacu (“pool, pond, lake”), as a result of lac's sudden spread in Old French. This was brought about following the annexation of English controlled Normandy into the kingdom of France in 1204. A full-out borrowing of the term from Middle English rather than from the Latin is also not an impossibility, as the earliest attestations of Old French lac are in the (written by Anglo-Saxon and Anglo-Norman scribes in England) and  (an Arthurian romance, whose author was heavily influenced by English, Anglo-Norman, and Celtic writings).

Lake in the present instance is simply a large body of water that is completely surrounded by land, which easily describes all of the big lakes in the Lake District regardless of location.

Dictionaries used

 * Middle English Compendium
 * Wiktionary