All 4 Uses

factor
in
Childhood's End
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We think we've got a reasonable idea of that-anyway it doesn't matter If we're out even by a factor often.†
Chpt 4 *

factor = thing that affects a result or outcome
Behind his decision there was another factor of which, he was unaware.†
Chpt 9
Given these factors, it is hardly surprising that he acted in the way he did.†
Chpt 9
Its establishment had taken twenty years and some billions of Pounds Decimal-a relatively trivial factor, therefore, of the world's total wealth.†
Chpt 15

Definitions:

(1) (factor as in: It was the deciding factor.)
something that affects a result or outcome

You also may encounter x-factor or x factor--meaning "the most important thing that influences a result or outcome."
(2) (factor as in: factor it into your thinking)
include consideration of
(3) (meaning too rare to warrant focus)
There are many specialized meanings in fields such as mathematics, business, finance, biology, and grammar.