Question

If we (meet) ....... him tomorrow, we'll say hello. What word is used instead of dots?

Answer 1

That word is meet.

According to the rule of first conditional type of sentences, the verb form in the clause part of the sentense is always V1 – a Present Simple one.

Answer 2

The word used instead of the dots in the sentence is "meet," making the complete sentence: "If we meet him tomorrow, we'll say hello."