cardigan vest
A cardigan vest is a cardigan without sleeves, resembling an open-fronted sweater vest, usually with buttons.
If a garment (like a jacket) is worn over the cardigan, so it is not clear if the cardigan has sleeves or not, simply tag it as cardigan, not cardigan vest.
Examples
NOT a cardigan vest
- Danbooru post #2493756: right: sweater vest not cardigan vest, left: cardigan vest
- Danbooru post #8660053: if a garment or pose covers up the sleeve length just use cardigan, not cardigan vest.