IPA: /ˈoʊvərˌsaɪz/
KK: /ˈoʊvərˌsaɪz/
Larger than what is normal or needed.
He bought an oversize shirt because he likes a loose fit.
A size that is larger than normal or typical.
The store offers a variety of clothing in oversize for those who prefer a looser fit.
Oversize → It is formed from "over-" (meaning excessively or beyond) and "size" (from Old French *size*, meaning dimension or magnitude). The word "oversize" means excessively large or beyond the usual size.
Think of something that is "beyond" its normal "size" — that's why oversize means larger than usual.