a notch in (someone's) belt

a notch in (someone's) belt

A remarkable success or achievement, especially one in a successive string, list, or tally of other such ones. (Can also be formulated as "a notch in the belt of (someone). The successful negotiation of the merger between the two companies was another notch in the young executive's belt. It wasn't a particularly difficult match, but the win is nevertheless a notch in the belt of the defending champion.
See also: belt, notch