All 10 Uses of

positive

in

Sense and Sensibility

This picture, she had allowed herself to believe, might have been accidentally obtained; it might not have been Edward's gift; but a correspondence between them by letter, could subsist only under a positive engagement, could be authorised by nothing else; for a few moments, she was almost overcome—her heart sunk within her, and she could hardly stand; but exertion was indispensably necessary; and she struggled so resolutely against the oppression of her feelings, that her success was…†
Chpt 22 (definition 1)

The name of Willoughby, John Willoughby, frequently repeated, first caught my attention; and what followed was a positive assertion that every thing was now finally settled respecting his marriage with Miss Grey—it was no longer to be a secret—it would take place even within a few weeks, with many particulars of preparations and other matters.†
Chpt 30 (definition 1)

Mrs. Jennings left them earlier than usual; for she could not be easy till the Middletons and Palmers were able to grieve as much as herself; and positively refusing Elinor's offered attendance, went out alone for the rest of the morning.†
Chpt 31 (definition 1)

Had both the children been there, the affair might have been determined too easily by measuring them at once; but as Harry only was present, it was all conjectural assertion on both sides; and every body had a right to be equally positive in their opinion, and to repeat it over and over again as often as they liked.†
Chpt 34 (definition 1)

Elinor avoided it upon principle, as tending to fix still more upon her thoughts, by the too warm, too positive assurances of Marianne, that belief of Edward's continued affection for herself which she rather wished to do away; and Marianne's courage soon failed her, in trying to converse upon a topic which always left her more dissatisfied with herself than ever, by the comparison it necessarily produced between Elinor's conduct and her own.†
Chpt 38 (definition 1) *

Elinor contradicted it, however, very positively; and by relating that she had herself been employed in conveying the offer from Colonel Brandon to Edward, and, therefore, must understand the terms on which it was given, obliged him to submit to her authority.†
Chpt 41 (definition 1)

Elinor's satisfaction, at the moment of removal, was more positive.†
Chpt 42 (definition 1)

…the readiness of the house, to which Colonel Brandon, with an eager desire for the accommodation of Elinor, was making considerable improvements; and after waiting some time for their completion, after experiencing, as usual, a thousand disappointments and delays from the unaccountable dilatoriness of the workmen, Elinor, as usual, broke through the first positive resolution of not marrying till every thing was ready, and the ceremony took place in Barton church early in the autumn.†
Chpt 50 (definition 1)

Uses with a very rare meaning:

I must do THIS justice to Mr. Willoughby—he has broken no positive engagement with my sister.†
Chpt 30 (definition 2) *

No positive engagement indeed! after taking her all over Allenham House, and fixing on the very rooms they were to live in hereafter!†
Chpt 30 (definition 2)

Definitions:

(1) (positive as in: I'm absolutely positive!)
certain (having no doubt; or used for emphasis)

(2) (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.