to weigh; weight; measure
Depicts a person (大) with a horn (角) on their head, indicating an unbalanced single horn as opposed to a balanced pair of horns. 行 represents the sound. The meaning later shifted to "to weigh" and "measure".
《說文》：“衡，牛觸，橫大木其角。从角，从大，行聲。《詩》曰：‘設其楅衡。’，古文衡如此。”