It's been a common practice for centuries to refer to fairies by euphemisms, terms that are intentionally more positive than the beings being referred to. I'm going to start a list here which I'll occasionally update of these terms and, where possible, the oldest known dates of their uses. This is a work in progress, if you have references to uses of any of these terms in specific dated works please share in the comments.
Irish*
Aes Sidhe [people of the fairy mounds, modern Aos Sidhe] circa 7th-9th century Echtra Condla
Gáethshluagh [host of the wind] circa 13th century Accalam na Senórach
Túathgeinte [leftwards turning folk] circa 16th century O'Davoren's Glossary
Sidaige [dweller in a fairy mound] circa 16th century O'Davoren's Glossary
Daoine Sidhe [people of the fairy mounds]
Daoine Uaisle [Noble People]
Na Uaisle [the Gentry]
Na huaisle bheaga [the little gentry]Daoine Maithe [Good People] in use by 19th century/early 20th, ref. Duchas.ie
Daoine Eile [Other People]
Slua Sí [fairy host] old or middle Irish Sidshlúag
An slua aerach [the host of the air]Slua sí an aeir [fairy host of the air]
Sióg [given as fairies, possibly sí + diminutive óg] probably 20th century^
Cuid na gcnoc [part of the hills]
Dream na gcnoc [people of the hills]
An dream aerach [the people of the air]
An bunadh beag [the little people]
Daoine beaga [the little people]
Scottish
Daoine Sith [people of the fairy hills or people of peace]
An Sluagh [fairy host]
Sleagh Maith [good people] ref 1691 rev Kirk
Scots
Gude nichtbouris [good neighbours] ref 1585 the Flyting Between Montgomerie and PolwartSubterranean ref 1691 rev Robert Kirk
Fairfolkis, fairy folk, ffair folk ref 1518 Douglas's Aenid translation; 1576 Ancient Criminal Trials in Scotland from AD 1488 to AD 1624
Gude Wichtis/Gude Wichts [good beings] ref 1576 Criminal Trials
Seelie Wicht [blessed being] as 'celly vichtys' 1564, William Hay; as 'sillyie wichts' 1572 Criminal Trials
Seelie Court [blessed company] 1783 ballad of Alison Gross
Seily Queen ref 1827 Crawfurd's Collection v II, A Fairie Sang
Unseelie Court** [unholy company] ref. 1819 Edinburgh Magazine and Literary Miscellany vol 84
Gentrie ref 1827 Crawfurds Collection v II, notes on 'A Fairie Sang'
Welsh
Tylwyth Teg/Tylwythen Deg [Fair Family] ref in the 12th century by Giraldus Cambrensis
Plant Annwn [children of the Otherworld]
Bendith Y Mamau [Mother's Blessing]
Manx
Guillyn Veggey [little boys]
Vooinjer Veggey/Dooiney Veggey [little people]~
Little Fellows
French^^
Les bonnes dames [the good ladies]English
Little People ref 1726 https://www.etymonline.com/search?q=little
Wee Folk ref 1819 https://www.etymonline.com/search?q=wee
Fairy (suggested as possible euphemism imported from French to avoid saying elves^^^)
Latin***
Pulchrum Populum [fair folk] ref 1586 Bromyard Summa Predicantium (originally 14th century text)
Misc./General
Gentle Folk
Gentry
Honest Folk ref 1908 Simpson Folk Lore in Lowland Scotland
Hill Folk ref 1908 Simpson
Silently Moving People, ref 1900 Campbell, Gaelic Otherworld
Still Folk ref 1900 Campbell
Themselves
Greenies
Greencoaties
Grey Neighbours (Orkney)
Othercrowd
Shining Ones
The Honest Folk (Scotland, ref Henderson)
The Forgetful People (Scotland, ref Henderson)
The Restless People (Scotland, ref Henderson)
*with thanks to Shane Broderick for many of the Irish terms. English translations and any errors in translating my own
^ per discussion with Shane Broderick
**Technically not a euphemism, as it is a negative term
~ related by Adam Cain via Twitter, 5/22
^^ thanks to Allie Valkyrie for the French terms and translations
***the Latin here was used by an English writer and in my opinion reflects English euphemism of the time
^^^ suggested by prof Ronald Hutton in a lecture 'Traditional Fairies' 21/9/21
References
Henderson & Cowan (2007) Scottish Fairy Belief
1908 Simpson Folk Lore in Lowland Scotland
1900 Campbell, Gaelic Otherworld
1586 Bromyard Summa Predicantium
12th century by Giraldus Cambrensis
1585 the Flyting Between Montgomerie and Polwart
Crawfurds Collection v II, notes on 'A Fairie Sang', 1827
1819 Edinburgh Magazine and Literary Miscellany vol 84
1576 Criminal Trials
1564, William Hay; as 'sillyie wichts' 1572 Criminal Trials
1783 ballad of Alison Gross
Echtra Condla
Accalam na Senórach
O'Davoren's Glossary
Robert Kirk, 1691, The Secret Commonwealth of Elves Fauns and Fairies