Rashi had ten methods to explain biblical meaning. Rashi would sometimes derive the meaning of a word from the meaning of its underlying Biblical root. Today's example illustrates this.

Verse Gn18-12b discussing Sarah's skepticism at having a child states ....after my menopause I will have periods. An literal translation of the same verselet would be ....after my withering I will have delights. The Hebrew word Ayin-Daleth-Nun-Hey meaning female youth, (pre-menopause) grammatically comes either from the root Ayin-Daleth-Nun, meaning delight, pleasure, or from the root Yud-Ayin-Daleth meaning date, time. In other words Rashi advances the idea that Youth / pre-menopause is the time of delight, pleasure. Similarly, Rashi advances the idea that Pre-menopause is the time of periods,dates, and times.

Advanced Rashi: Very often etymologies come in pairs. The idea is that even if a word had a primary etymology it very often by puns and inuendos achieves secondary etymologies. After a while both derivations become equally important.