1. (noun) A plaster is a small strip of adhesive tape with an antiseptic dressing. You stick it onto your skin if you cut yourself.
Sameera cut her finger on a knife, so she got a plaster from the first-aid box.
2. (noun) A building material that you put on a wall to make it smooth.
(verb) To plaster a wall means to put plaster on it to make it smooth. When you do this it’s called plastering.
Jeff plastered the walls of the bedroom before he painted it.