Rashi on Deuteronomy 2:6/רש"י על דברים ב׳:ו׳

1תכרו — This is an expression denoting purchase. Similar is (Genesis 50:5; see Rashi thereon), “which I have bought (כריתי) for myself”, for thus in the coast cities do they use for "trading” the term כירה (Rosh Hashanah 26a).