Move forward, progress, develop. For example, We stopped as soon as darkness began to come on. [Early 1600s]
Hurry up, as in Come on now, it's getting late. This imperative to urge someone forward has been so used since about 1450.
Also, come upon. Meet or find unexpectedly, as in We came on him while walking down the street, or I came upon an old friend in the bookstore today. [Second half of 1700s]
Make a stage entrance, as in After the next cue she comes on from the right. [Early 1800s]
Please oblige me, as in Come on, that's no excuse for leaving, or Come on, you'll really like this restaurant. [Colloquial; first half of 1900s]
Convey a specific personal image, as in He comes on like a go-getter but he's really rather timid. [Slang; c. 1940]
Also, come on strong. Behave or speak in an aggressive way, as in Take it easy; you're coming on awfully strong. [c. 1940]
Also, come on to. Make sexual advances, as in She reported her boss for coming on to her. This usage probably was derived from the earlier use of the noun come-on for a sexual advance. [Slang; 1950s]
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