button-down vs buttoned-down

button-down and buttoned-down both are adjectives.

Word	Noun	Adjective	Verb	Adverb
button-down	No	Yes	No	No
buttoned-down	No	Yes	No	No

As adjectives, button-down and buttoned-down are synonyms defined as:

Other synonyms of button-down include conservative.

button-down (adjective)	buttoned-down (adjective)
of a shirt; having the ends of the collar fastened down by buttons	unimaginatively conventional
unimaginatively conventional