Rashi would sometimes derive the meaning of a word from the meaning of its underlying Biblical root. In applying this method Rashi would use all available grammatical methods to study the meanings of related roots. The next paragraph presents one such rule.

In Hebrew, one indicates a feminine form by appending a suffix hey. Several masculine-feminine pairs are presented below:
• Tzedek means justice while Tzedakah, the feminine form, means charity.
• Aysh means fire while Isheh, the feminine form, means fuel. [Hence the frequently occuring phrase in the sacrificial procedures, describing sacrifices as bread, fuel, a pleasant scent, for the sake of God]
• Barar means to select while Barah, the feminine form, means something healthy and plump, the type of object that you prefer to select.
• Chom means hot while Chamah, the femine form, refers to the sun.
• KaLaL means complete while KaLaH, the feminine form, means both utensils and a bride, that which enables completion.

Advanced Rashi: We can just leave the list as masculine-feminine; but we can also see the pairs as speaking about enablement a characteristic frequently associated with females. Thus the bride completes her husband; the sun enables heat; something healthy will drive and facilitate selection (otherwise you won't want to select anything); the fuel enables and facilitates fire; finally, (remarkably) it is charity that facilitates justice. Justice thrives best when people are generally charitable; this makes it less likely for someone who deserves no mercy to receive strick justice.