WordNet sense 1 (of or relating to positivism):

positivist, positivistic

WordNet sense 2 (having a positive electric charge):

electropositive

WordNet sense 3 (indicating existence or presence of a suspected condition or pathogen):

confirming

WordNet sense 4 (on the positive side or higher end of a scale):

plus

WordNet sense 5 (emphasizing what is laudable or hopeful or to the good):

constructive

WordNet sense 6 (expecting the best):

affirmative

WordNet sense 7 (formally laid down or imposed):

prescribed

WordNet sense 8 (being in accord with established forms and conventions and requirements (as e.g. of formal dress)):

formal

WordNet sense 9 (impossible to deny or disprove):

incontrovertible, irrefutable

WordNet sense 10 (not possible to deny):

undeniable

WordNet sense 11 (marked by excessive confidence):

cocksure, overconfident

WordNet sense 12 (having or marked by confidence or assurance):

confident

WordNet sense 13 (persuaded of; very sure):

convinced

WordNet sense 14 (having or feeling no doubt or uncertainty; confident and assured):

certain, sure

WordNet sense 15 (giving an advantage):

advantageous