From *leit- (related to Latin lītus (“sea coast, beach”) < *leitos), from Proto-Baltic *lei-, *lie- with an extra -t, from Proto-Indo-European *ley-, *lī- (“to pour, to flow, to drip”). The stem was perhaps originally a reference to people from the "land of the rain" or "land of the rivers." It is also possible that there was an original river or lake name *Leitā, from which *leitā-tyā, *leityā > leiša, from which the nominative leitis could be derived.
leitis m (2nd declension, feminine form: leitiete)
- a (male) Lithuanian
strādnieki... kalpi, vai tie būtu vācieši, leiši, krievi, ebreji, mums draugi ― workers... servants, be they Germans, Lithuanians, Russians, Jews, are friends to us
- (genitive plural): Lithuanian, pertaining to Lithuania and its people
leišu valoda ― the Lithuanian language
Aspazija pieraksta leišu sakāmvardus un mīklas ― Aspazija recorded Lithuanian proverbs and riddles