The person, place, or thing from which something (information, goods, etc.) comes or is acquired.

Spring; fountainhead; wellhead; any collection of water on or under the surface of the ground in which a stream originates.

A reporter's informant.

(computing) Source code.

(electronics) The name of one terminal of a field effect transistor (FET).

(graph theory) A node in a directed graph whose edges all go out from it; one with no entering edges.

To obtain or procure: used especially of a business resource.

(transitive) To find information about (a quotation)'s source (from which it comes): to find a citation for.