Cases of word usage

1) a movable metal plate that regulates the flow of air, e.g. into a stove (damper)

2) to use a needle and acid to make (a picture) on a metal plate from which copies may be printed (etch)

3) a flat metal or stone plate fixed on a wall as a memorial; the yellow substance that forms on the teeth and causes decay (plaque)

4) a mark, object, symbol etc used to represent something: 'mathematical sings' such as '+', '-', 'x', '?'; a word or words, design etc on a board or plate to give a warning, or to give direction; to write (one's name) on (a letter, application form etc) (sign)