lókus
“body of still water, lake”lake, still water
PIE noun root for a body of still water or lake. Source of Latin lacus, English "lake," and words for standing water.
Discussion
*lókus is a Proto-Indo-European noun root meaning "body of still water" or "lake," one of the key hydrological terms reconstructed for the proto-language.
Latin lacus "lake, basin, vat" is the primary reflex, yielding English lake, lagoon (via Italian), and lacustrine. Greek lákkos "pond, cistern" shows a parallel development. Old Irish loch "lake" (as in Loch Ness) continues the Celtic reflex and is among the best-known survivals of this root.
In Germanic, Old English lacu "stream, pool" (which gives the -lake in English place names) and Old Norse lǫgr "liquid, lake" reflect the root, though English lake itself was borrowed from Latin or Celtic rather than inherited directly. Gothic lagus "water" confirms the Germanic presence.
The semantic core is standing or contained water, as opposed to flowing water (covered by roots like *srew- and *h₁reyH-). The PIE vocabulary distinguished carefully between different water types, suggesting a landscape with diverse aquatic features.
Modern descendants include English lake, lagoon, loch, and the Latin-derived lacustrine and lacuna.
Notes
Source of Latin "lacus", English "lake", Irish "loch". Widespread Wanderwort.