A telephone number not listed in the directory.

A burglar alarm that makes no noise that is audible to the trespasser.

(idiomatic) To think very strong thoughts that one wishes to yell out loud but does not.

A ham radio operator who has died.

plural of silent alarm

An auction where people write secret bids on a piece of paper, and whoever has the highest bid wins the item.

(music) An event at which people dance to music that is transmitted through wireless headphones rather than played over a speaker system.

(cinematography, retronym) A film with no synchronized recorded sound, especially spoken dialogue.

(economics, finance) A system of bartering, once common in Africa, in which traders remain silent, either because they have no language in common or because they both wish to keep secret and not discuss the origins of their goods (especially gold and salt).

plural of silent partner