Englishfor English speakers
action
Noun
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An action is something that you do, or something that happens, especially with motion.
At 3am, just west of the building, the plan was put into action.
There was a huge difference between my thoughts and my actions.
What they did was clearly wrong, but their actions were understandable.
The Health Authority is preparing to take legal action against the restaurants that fail to follow the regulations.
function
Noun
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Something or someone's function is its purpose or its job.
The army sometimes performs a policing function.
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A function is an organised event.
I met Sylvia at a church function last week.
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If mathX/math is a function of mathY/math, then mathX/math exists because of or is affected by mathY/math
The speed of the computer is a function of its main processor.
When you see, mathY=f(X)/math, you read it, "mathY/math is a function of mathX/math". Here the value of mathY/math depends on the value assigned to the variable mathX/math.
function
Verb
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If something is functioning, it is working and is not completely broken.
Her heart stopped, but her brain continued to function.
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If something functions as mathX/math, it does the job of mathX/math.
In this sentence, "sentence" functions as the subject.