Q: What would you say is more acceptable as a modifier, “old-fashion” or “old-fashioned”? One hears both interchangeably.
A: The usual form, and the only one accepted in standard dictionaries, is “old-fashioned.”
We did find a mention of “old-fashion” in one standard dictionary, the online Merriam-Webster Unabridged. But it says that “old-fashion” is an “archaic” term meaning “old-fashioned.”
Both versions are given in the Oxford English Dictionary, which is an etymological dictionary based on historical evidence.
The two adjectives are well established—they were first recorded in the 1590s—but “old-fashioned” is more frequent in current usage, the OED says.
The adjective “old-fashioned” is defined in the OED as “of or resembling a fashion or style belonging to an earlier time,” or “antiquated in form or character.”
In the dictionary’s earliest citation, the term describes an antique ship: “Out of the medyan center … did ryse vp an olde fashioned vessell, and verie beautifull.” (From a 1592 translation of Francesco Colonna’s Hypnerotomachia Poliphili, a romance originally written in Latinate Italian.)
The shorter adjective “old-fashion,” the OED says, means “resembling a fashion or style belonging to an earlier time.”
The dictionary’s earliest example comes only a few years later than the one mentioned above: “I sit like an old King in an old fashion play.” (From George Chapman’s comedy An Humerous Dayes Myrth, 1599.)
The two adjectives differ in their grammatical structure.
“Old-fashioned” combines “old” with the participial adjective “fashioned,” from the verb “fashion.”
“Old-fashion” combines “old” with the noun “fashion.” However, the OED notes that “in some instances” it is “perhaps shortened” from the longer version “by loss of the final consonant.”
We haven’t found much about these terms in usage guides. But the fact that standard dictionaries don’t recognize “old-fashion” is reason enough to prefer the longer version.
In fact, “old-fashioned” seems to have been the preference even in the 19th century.
We found this in George Crabb’s English Synonymes Explained (2nd ed., London, 1818): “OLD-FASHIONED signifies after an old fashion. … The manners are old-fashioned which are gone quite out of fashion . … The old-fashioned is opposed to the fashionable.”
from Grammarphobia http://www.grammarphobia.com/blog/2016/07/old-fashioned.html