From Middle English remembren, from Old French remembrer ("to remember"), from Late Latin rememorari ("to remember again"), from re- + memor, from Proto-Indo-European *mer-, *(s)mer-. Cognate with Old English mimorian, mymerian, Old English māmorian ("to deliberate, plan out, design"). More at mammer.
The success of the Old French word was helped by its proximity in sound and meaning to an existing Germanic word: Old English mimorian, mymerian from Proto-Germanic *mimrōną, *mīmrōną, from the same Indo-European source, and is akin to Saterland Frisian mīmerje ("to ponder, reflect"), Middle Low German mimeren ("to ponder, meditate"), Middle Dutch mimeren ("to reflect, think to oneself") (Dutch mijmeren ("to muse, reflect deeply")), Old English mimor ("mindful"), Old Norse Mímir, Mim, Old English māmrian ("to think out, design"). Related to mourn.
Displaced native Middle English ȝemuneȝen ("to remember"), from Old English ġemynegian ("to remember, remind"); Middle English minnen ("to remember, have in mind"), from Old Norse minna ("to remind"); Middle English munden, ȝemunden, from Old English ġemynd ("memory, remembrance"); Middle English ithenchen, ȝethenchen, from Old English ġeþencan; Middle English manien ("to remind, mention, remember"), from Old English manian ("to admonish, remind, mention").