WordNet sense 1 (subject or submissive to authority or the control of another):

subordinate

WordNet sense 2 (serving or acting as a means or aid):

instrumental, implemental

WordNet sense 3 (providing assistance or serving a useful function):

helpful

WordNet sense 4 (abjectly submissive; characteristic of a slave or servant):

slavish, submissive

WordNet sense 5 (submissive or fawning in attitude or behavior):

servile