1894 in the biological sense "repetition of parts in living things;" earlier in rhetoric, "synecdoche in which totality is expressed by contrasting parts" (such as high and low, young and old); from Modern Latin merismus, from Greek merismos "a dividing, division, a partition," from merizein "to divide," from meros "a part, a share" (from PIE root *(s)mer- (2) "to get a share of something"). Related: Meristic. Merismatic "dividing by the formation of internal partitions" is attested by 1849.
Proto-Indo-European root meaning "to get a share of something."
It is the hypothetical source of/evidence for its existence is provided by: Greek meros "part, lot," moira "share, fate," moros "fate, destiny, doom;" Hittite mark "to divide" a sacrifice; Latin merere, meriri "to earn, deserve, acquire, gain."