1.Definition: affirming or giving assent

"An affirmative decision", "Affirmative votes"

Related Adjective(s):affirmatory

2.Definition: expecting the best

"An affirmative outlook"

Related Adjective(s):optimistic

3.Definition: expressing or manifesting praise or approval

"An affirmative nod"

Related Adjective(s):approbative, approbatory, approving, plausive