Armhole
/ˈɑːrmhəʊl/
Definition 1 of 1
Pro Tip 1/3Clothing Fit
Refer to 'armhole' when discussing the fit of sleeves and shoulder comfort in clothing. 
The armholes on this jacket are too tight, restricting my movement.
Pro Tip 2/3Sewing Terminology
In sewing, 'armhole' describes the opening in a pattern or garment that the sleeve is attached to. 
Make sure to measure the armhole precisely before cutting the fabric.
Pro Tip 3/3Fashion Descriptions
'Armhole' is used in fashion to talk about the style and design of tops and dresses. 
The oversized armholes of her tank top gave it a relaxed, breezy look.