I’d support adding armscye. Admittedly, I’d never heard it until recently, but it’s a dressmaking term and, like the original poster, I’ve also come across it in knitting patterns, e.g. in the measurements for the sleeveless Pabaigh top by Kate Davies (https://www.shopkdd.com/pabaigh), the depth of the armhole is referred to as the ‘armscye depth’.

Merriam Webster:

arm·​scye | \ ˈärmˌsī, -ˌzī \

variants: or less commonly armseye \ -​ˌzī \

plural -s

Definition of armscye

: ARMHOLE specifically, in tailoring and dressmaking : the shape or outline of the armhole

Collins:

armscye in American English

(ˈɑːrmsai, -zai)

NOUN

the armhole opening in a garment

Also: armseye (ˈɑːrmzˌai)

Word origin

[arm1 + scye armhole (orig. Scot, Ulster dial. s(e)y, sie, of uncert. orig.); reanalyzed by folk etym. as “arm's eye”]

(Not sure why ‘in American English’ – the patterns I’ve seen it in weren’t in American English.)

https://www.businessoffashion.com/education/f...

Armscye (also spelt arm scythe and pronounced ‘Arm’s Eye’) is a Scottish term in origin. It refers to the armhole opening in a garment and is also the tailoring term for the pattern shape used when constructing the armhole. If you were to label the anatomy of a dress, the armscye would be at the opening of the bodice, where the sleeve is attached.

Langenscheidt gives Ärmelausschnitt

https://en.langenscheidt.com/english-german/a...

Ärmelausschnitt         armscye in dressmaking