one-step, one-strike distance
In kendo and other sword arts, the distance where taking one more step forward allows you to strike your opponent. Often used in the phrase 一足一刀の間合い.
Strike the men from the one-step, one-strike distance.
Compound of 一足 (one step) and 一刀 (one sword/strike), literally 'one step, one sword'. The exact historical derivation is uncertain, but the term is firmly established in kendo terminology.