Synonyms for Rudimentary (same or very similar meaning)
WordNet sense 1 (being or involving basic facts or principles):
fundamental, underlying
WordNet sense 2 (pertaining to or constituting a base or basis):
basic
WordNet sense 3 (not fully developed in mature animals):
vestigial
WordNet sense 4 (not developed):
undeveloped
WordNet sense 5 (not complete or total; not completed):
uncomplete
From the ODE community, based on WordNet
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