Definition of do for

The phrase "do for" originated in the late 19th century in British English, and its exact origins are somewhat unclear. It is possible that the term derives from the expression "do for" in the sense of "finish off" or "kill" someone, as this meaning of the phrase was in use at the time. However, the use of "do for" in its modern sense of "help" or "benefit" likely emerged as an extension of the British slang term "do for" to describe completing a task or fulfilling a need. In this context, "do for" came to imply the idea of meeting someone's requirements or doing something that would be of use to them. Over time, this meaning became so common in English usage that it supplanted the more grisly connotation associated with the phrase in earlier decades. Today, the expression "do for" is widely used in both British and American English to indicate that one has performed an action or task that has benefited someone else.