Rashi on Exodus 8:5/רש"י על שמות ח׳:ה׳

1התפאר עלי GLORY OVER ME — Similar is, (Isaiah 10:15) “Should the axe יתפאר against him that heweth therewith” i. e. should it boast, saying “I am greater than thou”; old French vanter. Therefore התפאר means pride yourself on showing your cleverness and on asking of me a difficult matter asserting that I shall be unable to do it.

2למתי אעתיר FOR WHAT PERIOD SHALL I ENTREAT FOR THEE — With reference to the entreaty which I shall make to-day regarding the destruction of the frogs, by what period do you wish that they should be destroyed, and you will see whether I can carry out my promise by the time which you will set me. If the text said מתי אעתיר (without ל), it would signify “when shall I pray?” but now that it is said למתי, it signifies I will pray to-day for you that the frogs should be destroyed by the time which you will set for me. Tell me, then, by what day you wish that they shall be destroyed. The words here, אעתיר and העתירו (v. 4) and העתרתי (v. 25) are Hiphil forms, and it does not say אֶעְתַּר and עִתְרוּ and וְעָתַרְתִּי (Kal forms) because wherever the root עתר is used it denotes to pray much (more lit. Rashi’s words signify “to multiply praying”, “to make much praying”), and just as one says אַרְבֶּה and הַרְבּוּ and וְהִרְבֵּתִי which all have the meaning of “causing an action to happen” (in this case, causing a thing to be much — our Hiphil conjugation), so one says אַעְתִּיר and הַעְתִּירוּ and וְהֵעְתַּרְתִּי “I increase”, “increase ye” and “I will increase” i. e. I will increase words. The passage which serves as evidence of the meaning of all these words is (Ezekiel 35:13) “וְהֵעְתַּרְתֶּם your words against Me” — which can only mean “Ye have multiplied” (being a transitive verb; cf. Rashi on Genesis 25:21).