Is there a specific verb for when a person goes "um" and "ah" while they are thinking what to say? [duplicate]

Often you hear people go "um" and "ah" (or alternatively "erm") while they are thinking what to say.

I have come across "um and ah" or "umming and ahing" but this sounds rather informal and colloquial.

I was hoping there is a more formal, single-word verb that describes this action.

I think the right word depends on what is going on for the speaker:

If they are naturally just not a fluent speaker, you'd probably say they are stammering, stuttering or faltering.

If they are nervous, you might say they are hesitating (or, again, faltering).

If they are being evasive, struggling to find words to avoid saying the wrong thing, you might say they are hemming and hawing, umming and ahhing or hesitating.

It's hard to neutrally describe a pattern of speech without imputing some kind of thought process.

My first thought is falter, applying the sense of "behave uncertainly" to speech:

"They ran in here and then... um..." The witness faltered in her testimony.

Merriam-Webster indicates the transitive form for this ("faltered her testimony"), but one could generally say that speech filled with these utterances is faltering or that the speaker is faltering. Note that this doesn't assume the speaker's intent -- thinking, procrastinating, waiting for a distraction to end the interaction, etc.

However, on second thought the right word may depend on the purpose or effect of the utterances. They fall into the category of speech disfluencies, which serve a large number of purposes (differing between languages and cultures which particular sounds are supposed to mean what): filling silence, indicating that the speaker is thinking, indicating that attention is being paid, and so on. In North America it would be perfectly reasonable for someone to say "ah" with purpose and confidence to express acknowledgement, or "um" to break into a conversation. While faltering describes the instances in which these utterances are used to indicate the speaker is thinking, it probably does not apply to every instance of the example sounds you gave.

Those specific types of words are called speech disfluencies, but that is not a verb used to describe what one is doing when they use those words.

This is a bit of a nebulous question since speech disfluencies are used in so many common situations that among some populations they can represent up to 20% of the total words used in everyday conversation.

Verbs used to describe what you are doing when using a disfluency could include :

• If you do not know what to say, and you are indicating to your audience that you are taking a moment to think about it, you may be pondering, considering, or contemplating.
• If you do not know what to say, and the silence is making you uncomfortable, you are fillering.
• If you do not know what to say, and you you are trying to buy time, you are delaying.
• If you know about what you are trying to say, but you have a neurogenic speech impediment that makes saying it difficult, you are stuttering or stammering. (Some cases of filtering may also be described this way)
• Stutters are often caused by duress; so, if it is caused by a stressful situation you may be faltering or cowering
• If you know what you want to say, but are unsure if you should say it, you are hesitating
• If you know what you want to say, but purposefully include the disfluency for dramatic effect, you may be emphasizing.
• If you are parroting another person's disfluencies you may be mirroring or mocking

Johns Hopkins Medicine's site says that saying words like "uh" often is called "cluttering".

If you do this, you "clutter" when you speak.

(hopkinsmedicine.org)

These words are fillers, pure and simple- the speech equivalent of wheat and fiber inserted into hotdogs because they are cheap materials. These words are similarly cheap as they require zero mental expenditure, but are aimed to give the appearance that the speaker has, like, you know, umm, totally something to say. @Nosajimiki has suggested fillering, which would seem the natural transformation of the noun to verb, but the word doesn't feel natural. I suggest padding which is a common verb connoting the addition of fillers, even in a linguistic context:

From Merriam-Webster unabridged: pad

2
a (1) : to expand or lengthen (as a book, magazine article, speech) by the insertion of additional material that is usually essentially superfluous and often extraneous to the point of being irrelevant and that is usually used merely to artificially bring the thing so expanded up to some desired size or length or that is used for some other usually equivocal purpose (as to add impressiveness, suggest intellectual depth, mask an otherwise distasteful theme) : inflate — often used with out

An example sentence by me: "The other answers are thoroughly padded with worthless fillers."

Granted, padding in writing or speech is not restricted to cheap fillers, as it is one of the oldest tricks employed by students doing homework at the 11th hour, discovering 17 ways to say the same thing in as many sentences. But it fits the bill.