Rashi on Genesis 18:12/רש"י על בראשית י״ח:י״ב

1בקרבה [SARAH LAUGHED] WITHIN HERSELF (or, REGARDING HER INSIDE) — She reflected on her physical condition, saying, “Is it possible that this womb shall bear a child, that these dried-up breasts shall give forth milk” (Midrash Tanchuma, Shoftim 18).

2עדנה means glistening flesh (skin), and so it is used in the Mishna (Menachot 86a): it makes the hair fall out and the skin smooth (מעדן).