All 4 Uses

positive
in
Wuthering Heights
(Edited)

And they have all turned to enemies in a few hours: they have, I'm positive; the people here.
p. 88.5

positive = certain
A positive labour of Hercules, I assure you!
p. 109.9 *

positive = absolute (used for emphasis)
She's all nerves, and she couldn't bear the surprise, I'm positive.
p. 111.8

positive = certain
He's as strong now as when he first came into the north; I'm positive of that.
p. 176.9

Definitions:

(1) (positive as in: I'm absolutely positive!)
certain (having no doubt; or used for emphasis)
(2) (positive as in: had a positive effect)
good or beneficial
(3) (positive as in: positive feedback from my boss)
approval or agreement
(4) (positive as in: a positive attitude)
optimistic (expecting or focusing on good things); or agreeable
(5) (positive as in: The test came back positive.)
found a condition or substance to be present
indicating the presence of something being tested for -- especially a disease, condition, or substance
(6) (positive as in: a positive number)
greater than zero (of a number)
(7) (meaning too rare to warrant focus)
See a comprehensive dictionary for less common meanings of positive including some in the fields of electricity, physics, chemistry, medicine, philosophy, and grammar. Note that most all senses of positive indicate that something is good or present.