Most francophone sources state that Allaire is a variant of
Hilaire, which ultimately comes from Latin
hilaris meaning "cheerful".
However, at least one French source states that the surname can also be of Breton origin, in which case it is ultimately derived from the name of the medieval Breton saint Alar/Alor of Quimper (died in 462 AD). This etymology should be possible for Breton bearers of the surname, and would also explain (at least partially) why the surname is most common in
Brittany.
Sources used:
•
https://fr.wikipedia.org/wiki/Allaire (in French)
• scroll down to the entry for Allaire at
http://jeantosti.com/noms/a3.htm (in French)
•
https://www.filae.com/nom-de-famille/allaire.html (in French)
•
http://www.geopatronyme.com/cgi-bin/carte/nomcarte.cgi?numero=0013536&periode=4 (in French; shows the distribution of the surname)
Forchta in biuonga quamon ouer mi, in bethecoda mi thuisternussi.
In ic quad: "uuie sal geuan mi fetheron also duuon, in ic fliugon sal in raston sal?"