i Register
In some senses, button-down is marked as idiomatic, colloquial. Watch for register when choosing this word.
adj
Of a collar, able to be buttoned down to the shirt, as over a necktie.
Serious; staid; businesslike.
Conservative; conventional; unimaginative.
noun
A shirt with a button-down collar
Wearing a stylish pink button-down with white pinstripes, Ozzie Guillen beamed about feeling like he had "come home" when he was presented Wednesday as the manager of the Miami Marlins.
A button-up shirt