Sforno on Genesis 5:29/ספורנו על בראשית ה׳:כ״ט

1זה ינחמנו, Lemech prayed that this son would provide him with the ability to take a rest from his heavy labour. The root of the word נח is מנוחה, rest, (retirement). The word is also used in connection with giving one a respite from one’s enemies, as in Esther 9,16.