PIE base ‘to learn’, related to *men-¹ ‘to think’ and *dhē- ‘to do’.
Other derivatives include mathematical, polymath ‘a person of wide knowledge or learning’, from Greek polus ‘much, many’, from PIE base *pelə-¹ ‘to fill’, and opsimath ‘one who learns late in life’, from Greek opse ‘late, after a long time’, from PIE base *epi-.
[Pokorny *mendh- ‘to pay attention to; vivacious; wisdom’, p. 730.]