iuxta

Latin

Unclear, but reflects an earlier ablative form. Proposals include:^[1]^[2]

from Proto-Italic *jougestos (“yoked”), from *jougos (“team of yoke animals”) (whence Latin iūgera pl), from Proto-Indo-European *(H)yewg-es-, from *(H)yewg- (“join together”);
from Proto-Italic *jugistos (“closest”), equivalent to *(H)yug- +‎ *-istHos (“superlative suffix”); however, this suffix is otherwise not found in Latin.

The accusative is from the suffix used adverbially.

(Classical Latin) IPA^(key): /ˈi̯uːk.staː/, or IPA^(key): /ˈi̯uk.staː/,
(modern Italianate Ecclesiastical) IPA^(key): /ˈjuk.sta/,
Note: the length of the /u/ is uncertain due to lack of graphic attestations, unclear etymology and common conflation with iūstus (“just; exact”) already in Latin as well as its Romance descendants. Most other dictionaries list it as short.

iū̆xtā (not comparable)

iū̆xtā (+ accusative)

Borrowings:
- →⇒ French: juxtaposer
  - → English: juxtapose
- →⇒ Spanish: yuxtaponer (“juxtapose”)
Italo-Romance:
- Italian: giusta
Sardinian:
- Campidanese: giusta
- Logudorese: justa
- Nuorese: justa
Gallo-Romance:
- Old French: joste (“close to, along”)
  - French: jouxte (“close”) (semi-latinized, archaic)
- Old Occitan: josta
Vulgar Latin:
- ⇒ *iuxtāre
  - Catalan: justar ⇒ ajustar
    - → Spanish: ayustar (“splice (rope)”)
  - Old French: joster (“meet in battle, joust, be close to”) ⇒ ajoster (“add”)
    - French: jouter (“joust”), jouxter (“be close to”) (semi-latinized), ajouter (“add”)
    - Norman: joster (“play”) ⇒ jostoux (“happy”), ajoûter (“add”)
    - → English: joust
    - → Italian: giostrare (“joust”)
    - → Portuguese: justar (“joust”)
    - → Spanish: justar (“joust”)
  - Old Occitan: jostar ⇒ ajostar

Walther von Wartburg (1928–2002) “jŭxta”, in Französisches Etymologisches Wörterbuch, volume 5: J L, page 96
Walther von Wartburg (1928–2002) “jŭxtare”, in Französisches Etymologisches Wörterbuch, volume 5: J L, page 97
Rubattu, Antoninu (2006) “secondo”, in Dizionario universale della lingua di Sardegna, 2nd edition, Sassari: Edes

^ De Vaan, Michiel (2008) Etymological Dictionary of Latin and the other Italic Languages (Leiden Indo-European Etymological Dictionary Series; 7)‎, Leiden, Boston: Brill, →ISBN
^ Weiss, Michael L. (2009) Outline of the Historical and Comparative Grammar of Latin‎, Ann Arbor: Beech Stave Press, →ISBN, § B 1 b, page 357

“juxtā”, in Charlton T. Lewis and Charles Short (1879) A Latin Dictionary, Oxford: Clarendon Press
“iuxta”, in Charlton T. Lewis (1891) An Elementary Latin Dictionary, New York: Harper & Brothers
iuxta in Charles du Fresne du Cange’s Glossarium Mediæ et Infimæ Latinitatis (augmented edition with additions by D. P. Carpenterius, Adelungius and others, edited by Léopold Favre, 1883–1887)
juxtā in Gaffiot, Félix (1934) Dictionnaire illustré latin-français, Hachette.
iuxta in Ramminger, Johann (2016 July 16 (last accessed)) Neulateinische Wortliste: Ein Wörterbuch des Lateinischen von Petrarca bis 1700‎, pre-publication website, 2005-2016
"iūxtā" in Karl Ernst Georges, Ausführliches lateinisch-deutsches Handwörterbuch
Allen and Greenough's New Latin Grammar for Schools and Colleges Founded on Comparative Grammar, Ginn & Company, 1903, page 130.
Dirk Panhuis, Roland Hoffmann (translator), Lateinische Grammatik, Walter de Gruyter, 2015, pages 84 and 86.
"iūxtā" in PONS, Deutsch-Latein-Wörterbuch (German-Latin dictionary)