sienior
The term "sienior" is not a recognized word in the English language and does not appear in standard dictionaries or common usage. It is possible that "sienior" is a misspelling of a similar-sounding word, or it may be a neologism or a term specific to a particular context, such as a fictional work, a specialized jargon, or a personal invention.
If "sienior" was intended to be a misspelling of "senior," then it would refer to someone who
Alternatively, "sienior" might be a portmanteau or a deliberately altered word. Without further context or clarification