Is certificate a hypernym of diploma? This question came up in comments on another ELL question (here). I had considered the two synonymous, with some overlap in meaning. E.g. A diploma is a certificate issued by a university.
Notice that example has nearly identical wording to the definitions provided for diploma both by Google's dictionary, and Wikipedia. However, several dictionaries avoid the use of certificate to define diploma, e.g. Cambridge Dictionary. Others still use the word certified in the definition of diploma, e.g. Dictionary.com. This last definition, while not using the word certificate would still support the case of certificate as hypernym. After all, a diploma is a signed or certified document officially attesting to some achievement.
On the other hand, we have common educational usage, where the two words have different interpretations. E.g. This nice page from the University of the Potomac, "Certificate vs Diploma vs Degree".