1) Feature of a tee 2) Garment feature 3) Garment opening 4) Hole 5) Opening on the side of a vest 6) Part of a muscle shirt 7) Shirt opening 8) Shirt part 9) Sleeve feature 10) Sleeve opening 11) Sleeveless shirt feature 12) Sweater opening 13) Tank top feature 14) Tee shirt opening 15) Top opening Found on https://www.crosswordclues.com/clue/armhole
Arm'hole` noun [ Arm + hole .] 1. The cavity under the shoulder; the armpit. Bacon. 2. A hole for the arm in a garment. Found on http://www.encyclo.co.uk/webster/A/121