surname, at

于 depicts a stream of breath or qi rising upward but bending and twisting due to obstruction. Its original meaning is depletion or loss, which later extended to convey the sense of sighing or exclamation; this meaning was subsequently taken over by the character 吁. Since the breath is obstructed and lingers without dispersing, 于 also carries the meaning of “at”. Additionally, 于 is a variant form of 亏, and nowadays it is mostly used as a surname.