Why does my dad (95) just keep saying the same word all day long? And appears as though he doesn't even know he's doing it.

My 95 yr. Old Dad had a stroke 5 years ago, lost some vision and some memory, both have been slowly get worse every since, for the last few months he just keeps repeating the same word, its what he calls my Mom, Honey, ( by the way mom is still alive also)
But he sits and says honey over and over all day. Sometimes he sounds desperate, other times its like he is just saying it.  He can say other words he can still carry on some what of a convo. He does have a hard time finding and using the right words alot. But unless someone is talking to him or paying attention to him, or he is sleeping, he just keeps saying same word over and over, I have asked him what he needs mom has asked him, he doesn't know, but he won't stop. It's driving my mother insane. And I hate to just keep him doped up so he will stop. Any ideas or advice welcome. And Merry Christmas everyone.