Rashi on Leviticus 26:39/רש"י על ויקרא כ״ו:ל״ט

1בעונת אבתם אתם means if the iniquities of their fathers shall be with them, i. e. if they hold fast to (imitate) the doings of their fathers (cf. Sifra, Bechukotai, Chapter 8 2; Sanhedrin 27b).

2ימקו — This is an expression denoting “melting away” and therefore means the same as ימסו, “they shall melt away”. Similar to it are (Zechariah 14:12) “[their eyes] shall melt away (תמקנה) in their holes”; (Psalms 38:6) “My wounds נמקו, melt” (i. e. run with pus).