mid-14c., remembren, "keep (something or someone) in mind, retain in the memory," from Old French remembrer "remember, recall, bring to mind" (11c.), from Latin rememorari "recall to mind, remember," from re- "again" (see re-) + memorari "be mindful of," from memor "mindful" (from PIE root *(s)mer- (1) "to remember").
Meaning "recall to mind" is late 14c.; sense of "to mention" is from 1550s. Also in Middle English "to remind" (someone), "bring back the memory of" (something to someone); "give an account, narrate." An Anglo-Saxon verb for it was gemunan. The insertion of -b- between -m- and a following consonant (especially where a vowel has dropped out) is regular: compare number (n.), chamber (n.), humble (adj.).