A steadier ground guide to the word that will not come. What is failing, what actually helps in the moment, and how to tell this apart from a stroke. If the difficulty started suddenly, within minutes or hours, stop reading and call 911.
Notice your own urge to finish the sentence for him. That urge comes from love and impatience at the same time, and one breath is usually the difference between helping him find the word and taking it from him.
Before anything else, the timescale is the whole question. Word-finding trouble that came on over months is the illness. Word-finding trouble that arrived this morning is a stroke until proven otherwise, and it is a 911 call even if it has already passed.
The clinical word for the everyday version is anomia, meaning the word will not come although he knows exactly what he wants to say. It shows up as circling the target, describing the thing instead of naming it, calling a fork a spoon, or speech that flows normally and carries less and less. Nouns and names go first. What is failing is retrieval rather than intelligence, and he generally knows the difference, which is most of where the frustration comes from.
Later, comprehension joins it, and the two together are aphasia. Families often read the comprehension problem as not listening, or as the person having gone further than he has, when someone who cannot follow a long sentence may follow a short one perfectly.
There is a version where language leads rather than follows. Primary progressive aphasia is a language-led dementia, usually beginning somewhere between the forties and the sixties, in which words go while memory stays comparatively intact. It is often missed, and it is worth understanding what the label means: PPA describes what is failing first rather than which disease is doing it. Sometimes the underlying disease is frontotemporal degeneration, and in the variant where words come slowly and sentences are hard to repeat back it is most often Alzheimer's itself. Being told this is Alzheimer's is not necessarily a mistake. What matters is that whoever treats him knows the language went first.
Insight is usually preserved well into this illness, meaning he knows precisely what is happening to him, and depression severity and language severity track each other closely. That has two consequences, and both belong on this page. One is that his frustration is not confusion, it is grief. The other is in the red flags below.
Hearing belongs here too, since an uncorrected hearing loss looks a great deal like a comprehension problem and is the cheapest thing on the list to fix.
Change the conditions around the conversation, since that helps more reliably than anything you can do inside it.
Note when it is worst, since it is rarely constant. Fatigue, noise, being put on the spot and being asked direct questions in front of other people all make it worse, which lets you move the conversations that matter to the morning and the quiet room. Note also whether the loss is holding steady or moving, and whether it has ever arrived abruptly, since a sudden step down is a different event from a slow slope.
There is one thing here that is time-limited. While he still has the words, get the paperwork done: health care proxy, advance directive, powers of attorney, access to the accounts. Not because the end is near, since survival is measured in years, but because in this illness the ability to say what he wants goes before the ability to know what he wants. Ask him now, while asking is still a conversation, and record his voice if he will let you. And your own frustration is not a character failing. Waiting through a silence while someone you love struggles for a word is genuinely hard, and finishing his sentence is the kindest-feeling thing to do and often the wrong one. A conversation where the word never arrived and neither of you gave up is a conversation that went well.