So, as I was reading along, the word "linthead" was used several times. Then it was explained! Here's that passage:
"Charlie was a fling, as far as she was concerned. Charlotte was pretty shaken up when that wastrel, Liz's father, decided he didn't want to be a father after all. She went through a wild-divorcee period and got involved with a number of men whom Mother and Father disapproved of. Charlie was one of them. She never considered marrying him. The way she saw it, he was just a linthead."
"What's that?" I'd heard Mom use the word, but I didn't know what it meant.
"A millworker. They come off their shifts covered in lint."
Isn't that perfect!? I think so.