Rashi had ten methods to explain meaning. One method is the use of the common literary methods available to all languages. The metonymy-synecdoche method names items by good examples of them or by strong characterisics of them. Some common examples in English might be the use of the word honey to refer to any sweet thing or the use of the fruit orange to refer to any object with that color or the word heat to refer to any strong emotion - like the sexual and temper emotions. In each case, a word with a very specific meanning takes on a general reference to anything with those characteristics.

Applying this method to the sphere of emotions we see that the word thirsty would refer to acts done under strong emotions - with passion and premeditation - while the contrastive word full would refer to just eating and eating out of habit. Hence Rashi translates Dt29-18, When he [the person toying with worshipping idols] hears the words of the Torah he talks himself into believing that 'I will be allright' - I can go straight with my hearts desire; [and he does this] in order to add to his habitual sins, sins of passion and premediatation. Here Rashi translates the biblical word thirsty as meaning with passion and premeditation and similarly Rashi translates the biblical word full as meaning habitual sins.

Advanced Rashi: I was first asked the meaning of this Rashi about 3 years ago by someone whose house I frequent on Shabbath and holidays. My explanation at the time, I was told, appeared Midrashic. I was asked the meaning of the verse again today. I realized that the reason the Rashi appears Midrashic is the difference between the Talmudic and Biblical period. The Talmudic period uses the terms sins of passion and sins to anger [God]. A person use to these terms who sees the Biblical terms - thirsty, full - is apt to think of the verse as poetic and devoid of the precision that Talmudic terms have. Not so! The Biblical categories are different than the Talmudic categories!!! The word thirst includes both sins of passion and sins to anger (thirsty people may use violence to meet their needs). The contrast to passion-anger is force-of-habit. True the bible uses metonomy: thirst is a good example of passion-anger and eating to fullness is a good example of force of habit. But this is no more poetic than using the term honey to mean sweet or the fruit orange to refer to the color. In fact the Bible at Dt29-18 is describing the psychological transition from habitual sin to willful sin. It is also interesting that the Bible combines sins of passion and anger while the Talmudic period does not. There is certainly more to research here but we suffice with the above remarks.