aquarelle (n.)

*akwā-, Proto-Indo-European root meaning "water."

It forms all or part of: aqua; aqua-; aqua vitae; aqualung; aquamarine; aquanaut; aquarelle; aquarium; Aquarius; aquatic; aquatint; aqueduct; aqueous; aquifer; Aquitaine; eau; Evian; ewer; gouache; island; sewer (n.1) "conduit."

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit ap "water;" Hittite akwanzi "they drink;" Latin aqua "water, the sea, rain;" Lithuanian upė "a river;" Old English ea "river," Gothic ahua "river, waters." But Boutkan (2005) writes that only the Germanic and Latin words are sure, Old Irish ab is perhaps related, and "the rest of the evidence in Pokorny (1959) is uncertain."