alga.

Of unknown origin, though probably a foreign substrate loanword related to ulva (“various grass-like or rush-like aquatic plants”). Note also similar dubiously-related forms in Baltic and Germanic with connotations of filth and dirtiness, including Lithuanian el̃mės, almens (“ichor, sanies”), (dialectal) Norwegian ul (“moldy”), olga (“to loathe”), elgja (“to fell like vomiting”), ulma (“to get moldy”), Middle Low German olm, ulm (“rottenness (esp. of wood)”), and Dutch uilig (“moldy (of wood)”). These terms have been tentatively linked to a Proto-Indo-European *alg-, *alǵ- (“to be dirty, be slimy; frog; duckweed”); other similar forms include dialectal Norwegian alka (“to dirty, soil”), Norwegian ulk (“frog, slime”), Low German ulk (“frog”). That said, it is possible that the Baltic and Germanic are not related to the Latin, or that all the terms derive from the same substrate.