Both Uses

factor
in
Middlemarch
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He was an ardent fellow, but at present his ardor was absorbed in love of his work and in the ambition of making his life recognized as a factor in the better life of mankind—like other heroes of science who had nothing but an obscure country practice to begin with.†
Chpt 2 *

factor = thing that affects a result or outcome
I never heard but one worse roarer in my life, and that was a roan: it belonged to Pegwell, the corn-factor; he used to drive him in his gig seven years ago, and he wanted me to take him, but I said, 'Thank you, Peg, I don't deal in wind-instruments.'†
Chpt 3

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.