button-down

[ buht-n-doun ]
/ ˈbʌt nˌdaʊn /

adjective

(of a shirt collar) having buttonholes so it can be buttoned to the body of the shirt.
(of a shirt) having a button-down collar.
(of a shirt) having buttons down the front from the collar to the bottom.
Also buttoned-down. (especially of attitudes, opinions, etc.) extremely conventional; unimaginative.

Origin of button-down

An Americanism dating back to 1930–35

British Dictionary definitions for button down

button-down

adjective

(of a collar) having points that are fastened to the garment with buttons
(of a shirt) having a button-down collar
Also: buttoned-down conventional or conservative a button-down corporate culture