Definitions

1. verb

to release or open the fastening of (a garment, especially a shirt or collar)

“She unbuttoned her coat and put it on the chair.”

2. verb

to remove the buttons from (a garment)

“He unbuttoned the shirt and threw it in the laundry basket.”

3. verb

to relax or become less formal

“He unbuttoned his suit and joined the party.”

4. noun

the act of unfastening a button

“The unbuttoning of her coat was a subtle gesture.”