From an- +‎ dess (“right, south”).

andes

from the right
from the south
on the south [with do ‘of’]
- c. 800–825, Diarmait, Milan Glosses on the Psalms, published in Thesaurus Palaeohibernicus (reprinted 1987, Dublin Institute for Advanced Studies), edited and with translations by Whitley Stokes and John Strachan, vol. I, pp. 7–483, Ml. 67^d14
  Amal rund·gab slíab Sión andes ⁊ antúaid du⟨n⟩ chath⟨raig⟩ dïa dítin, sic rund·gabsat ar ṅdá thoíb du dítin ar n-inmedónach-ni.
  As Mount Sion is located on the south and the north of the city to protect it, so are our two sides there to protect our insides.

Middle Irish: anes, aness
- Irish: aneas
- Manx: niass
- Scottish Gaelic: a deas

Gregory Toner, Sharon Arbuthnot, Máire Ní Mhaonaigh, Marie-Luise Theuerkauf, Dagmar Wodtko, editors (2019), “andess”, in eDIL: Electronic Dictionary of the Irish Language

Asturian

Galician