Synonyms for Elementary (same or very similar meaning)
WordNet sense 1 (of or being the essential or basic part):
elemental, primary
WordNet sense 2 (pertaining to or constituting a base or basis):
basic
WordNet sense 3 (easy and not involved or complicated):
simple, uncomplicated, unproblematic
WordNet sense 4 (posing no difficulty; requiring little effort):
easy
From the ODE community, based on WordNet
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