The only free and comprehensive online etymological dictionary of the Spanish language
luego (Adverb) "soon," "then," "later"
10th cent. From Latin loco "at the time," ablative form of locus "place." Old Latin stlocus. From Proto-Italic *steloko- 'id.' From Proto-Indo-European *stel- "to place" with an unknown suffix *-oko-.
Indo-European
Romance
Asturian lueu, French louer, Italian locare
Basque
Basque leku "place" (borrowed from *lueko in a Romance language)
lugar m. (Noun) "place;" "room"
10th cent. Old Spanish locar. From Late Latin localis 'id.,' from Latin locus "place" (see luego).
Indo-European
Romance
Asturian llugar, Portuguese lugar, Galician lugar, Catalan locar, French local
luna f. (Noun) "moon"
10th cent. From Latin luna 'id.' Old Latin losna. From Proto-Italic *louksnā- 'id.' From Proto-Indo-European *leu̯k-s-nh2- "bright." From the root *leu̯k- "to shine" (see luz).
Also the origin of the surname Luna, indicating that the person hailed from one of the towns called Luna (there is one in Zaragoza, Alava, Albacete, and Leon).
Indo-European
Romance
Asturian lluna, Portuguese lua, Galician lúa, Catalan lluna, French lune, Italian luna, Aromanian lunã, Romanian lunã, Sardinian luna
Celtic
Old Irish lúain "Monday"
Balto-Slavic
Old Prussian lauxnos "stars"
Hellenic
Ancient Greek λύχνος (lykhnos) "lamp"
Indo-Iranian
Avestan raoxšna- "light"
At a very late date of Proto-Indo-European in the north-west we see a pre-form *louk-s-neh2- develop meaning "moon." This replaced the older Proto-Indo-European name for the moon based on "to measure" *meh1-, as the month was marked in moons.
lupa f. (Noun) "magnifying glass"
14th cent. Borrowed from French loupe 'id.' The earlier meaning in Middle French was "imperfectly transparent gem," which itself evolved from an older meaning of "iron clod." From Frankish *luppa "lump." Of unknown origin.
Indo-European
Germanic
Old English lobbe "spider," Frisian lobbe "lump of flesh"
luz f. (Noun) "light"
13th cent. From Latin lux 'id.' From Proto-Italic *louk- 'id.' From Proto-Indo-European *leu̯k- "to shine."
Indo-European
Romance
Asturian lluza, Portuguese luz, Galician luz, Italian luce, Sardinian luche
Germanic
Gothic liuhaþ "light," Old Norse ljóss "bright," Old High German lioht "light," Old English lēoht 'id.' (English light)
Balto-Slavic
Russian luč "ray," Czech louč "torch," Slovene lúč "light (from a fire)," Old Prussian luckis "torch"
Hellenic
Ancient Greek λευκός (leukós) "light"
Armenian
Armenian lowc'anem "to lighten"
Indo-Iranian
Sanskrit rócate "to shine," Young Avestan raocaiia- "to make shine"
Tocharian
A luk- "to shine," B luk- 'id.'