Hence, something occurring or done in the afternoon; esp., an afternoon meal; supper; also, an afternoon nap; a siesta. [
1913 Webster]
"Another great supper, or undermeal, was made ready for them, coming home from ditching and plowing."
[1913 Webster]
"I think I am furnished with Cattern [Catharine] pears for one undermeal."
[1913 Webster]
"In a narrower limit than the forty years' undermeal of the seven sleepers."
[1913 Webster]