This word is used here to mark a change from the story to information about [Abimelech](rc://en/tw/dict/bible/names/abimelech). (See: [[rc://en/ta/man/translate/writing-background]])
This is a polite way of saying he did not have sex with her. AT: "[Abimelech](rc://en/tw/dict/bible/names/abimelech) had not slept with Sarah" or "[Abimelech](rc://en/tw/dict/bible/names/abimelech) had not touched Sarah" (See: [[rc://en/ta/man/translate/figs-euphemism]])
Here "nation" stands for the people. [Abimelech](rc://en/tw/dict/bible/names/abimelech) is worried that God will punish not only him, but his people also. AT: "even a people who are innocent" (See: [[rc://en/ta/man/translate/figs-metonymy]])