unbuttoned

adj

Etymology: From un- + buttoned. In some instances possibly from unbutton.

1. Having the buttons undone.

   “Once a white man in an unbuttoned uniform, camping on the path with an armed escort of lank Zanzibaris, very hospitable and festive, not to say drunk.”

2. In disarray.
3. Informal, casual.

verb

1. simple past and past participle of unbutton

   “I unbuttoned my shirt to take it off.”