Both Uses of

factor
in
Middlemarch

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)
meaning too rare to warrant focus:

See a comprehensive dictionary for other meanings. Less common meanings include one that has to do with units of measurement. More specialized meanings are used in fields including mathematics, business, finance, biology, and grammar.