From Middle English rare, from Old French rare, rere, from Latin rārus, from Proto-Indo-European *er(e)-, *rē-. Replaced native Middle English gesen (from Old English gǣsne), Middle English seld (from Old English selden), and Middle English seldscene (from Old English seldsēne).
From a dialectal variant of rear, from Middle English rere, from Old English hrēr, hrēre, from hrēran, from Proto-Germanic *hrōzijaną, from Proto-Indo-European *ḱroHs-. Related to Old English hrōr. More at rear.