/ rʌnt; NAmE / noun
1.
the smallest, weakest animal of the young that are born from the same mother at the same time :
the runt of the litter
2.
( informal , disapproving ) a rude way of referring to a small, weak or unimportant person
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WORD ORIGIN
early 16th cent. (in the sense old or decayed tree stump ): of unknown origin.