thumbhole

noun

1. A hole designed to receive a thumb.

   “The paint set is the top-of-the-line model, the Extra-Fine Oil Artist’s Box with a 39-tube spectrum of colors, 6 different painting mediums, 10 brushes (5 sable and 5 hog bristle), palette knives and a palette (with old-fashioned thumbholes), all in a portable walnut box.”

verb

1. (transitive)To cut thumbholes (for carrying) in the lids of boxes.