The person searching for a word may have a clear thought waiting behind it.

A pause in the middle of a sentence is easy to read as confusion, and it usually is not. Word-finding is a separate mechanism from thinking, and it lags for all sorts of reasons: tiredness, a second language, age, or an idea more precise than the vocabulary within reach. Filling the gap for someone can feel like help and lands as impatience.

Let the silence run a few seconds longer than feels comfortable. Supply a word only if they ask or look to you. What arrives after the pause is often better than what you would have offered.