terrenus

Latin

Perhaps from Proto-Italic *terzeznos, from *terzos +‎ *-nos, the first of which from Proto-Indo-European *tersos, neuter s-stem to the root *ters- (“dry”).^[1]
Alternatively, from the locative form *terrai of terra and -nus.^[2]

terrēnus (feminine terrēna, neuter terrēnum); first/second-declension adjective

	masculine	feminine	neuter	masculine	feminine	neuter
	singular			plural
nominative	terrēnus	terrēna	terrēnum	terrēnī	terrēnae	terrēna
genitive	terrēnī	terrēnae	terrēnī	terrēnōrum	terrēnārum	terrēnōrum
dative	terrēnō	terrēnae	terrēnō	terrēnīs
accusative	terrēnum	terrēnam	terrēnum	terrēnōs	terrēnās	terrēna
ablative	terrēnō	terrēnā	terrēnō	terrēnīs
vocative	terrēne	terrēna	terrēnum	terrēnī	terrēnae	terrēna

Asturian: terrenu
Catalan: terreny, terrè
Corsican: tarrenu, terrenu
English: terrenal, terrene
French: terrain
- → English: terrain
Friulian: teren
Italian: terreno
Leonese: tarreno, tarrenu, tarrén
Occitan: terran, terren
Old Galician-Portuguese: terreo, tarreo, terrẽo, terreno
- Fala: terrenu
- Galician: terreo, tarrén, tarreo, tarreu
- Portuguese: terreno (see there for further descendants)
Romanian: teren
Sicilian: tirrenu
Spanish: terreno
Venetan: taren, teren

^ Walde, Alois; Hofmann, Johann Baptist (1954), “terrenus”, in Lateinisches etymologisches Wörterbuch (in German), 3rd edition, volume II, Heidelberg: Carl Winter, page 674
^ De Vaan, Michiel (2008), “terra”, in Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7), Leiden, Boston: Brill, →ISBN, page 616: “Derivatives > line 2 > terrēnus”

“terrēnus”, in Charlton T. Lewis and Charles Short (1879), A Latin Dictionary, Oxford: Clarendon Press
“terrēnus”, in Charlton T. Lewis (1891), An Elementary Latin Dictionary, New York: Harper & Brothers
"terrenus", in Charles du Fresne du Cange, Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
“terrēnus”, in Gaffiot, Félix (1934), Dictionnaire illustré latin-français, Hachette, pages 1,560–1.
“terrēnus” on page 1,928 of the Oxford Latin Dictionary (1st ed., 1968–82)
Niermeyer, Jan Frederik (1976), “terrenus”, in Mediae Latinitatis Lexicon Minus, Leiden, Boston: E. J. Brill, page 1,024/1