וַיֹּאמְר֥וּ אֵלָ֖יו לֹ֣א אֲדֹנִ֑י וַעֲבָדֶ֥יךָ בָּ֖אוּ לִשְׁבָּר־אֹֽכֶל׃
And they said unto him: ‘Nay, my lord, but to buy food are thy servants come.
Rashi on Genesis
לא אדני NAY, MY LORD — do not say this, for behold ועבדיך באו לשבר אכל THY SERVANTS HAVE COME TO BUY FOOD.
Or HaChaim on Genesis
ויאמרו אליו לא אדוני, They said to him: "No sir, etc." They said; 1) There is no reason to suspect us of spying even if we had come without a specific purpose. [I believe the author derives this from the tone-sign tipcha under the word באו; we would have expected the tone-sign mercha Ed.] 2) "In fact your servants have come to purchase food." They presented the purpose of their presence to buy food as the most natural explanantion for their journey to Egypt.
Radak on Genesis
ועבדיך, the letter ו at the beginning of this word substitutes for the word אבל, “but”. In other words: “no my lord, not as you have said; but your servants simply came here to buy food.” The use of the letter ו instead of the word אבל is not unique, as it also occurs in Psalms 7,5 ואחלצה צוררי ריקם, “but I have rescued my foe without reward.”