Here's how "quasi" is used in English:
* Quasi-official: Meaning something that has some official characteristics but is not fully official.
* Quasi-legal: Meaning something that is similar to a legal situation but not fully legal.
* Quasi-contract: A legal term for an agreement that is not a formal contract but is treated as one by the courts.
Example:
* "The organization was a quasi-governmental body." (It had some government functions but wasn't a full government agency.)
If you encountered "qua si" in a specific context, please provide more information, and I'll be happy to help you understand its meaning.