The phrase "most quintan" refers to something that is the most breakable or fragile. There are plenty of synonyms that can be used to describe this kind of object or material. Some of the most common synonyms include delicate, brittle, frail, fragile, and vulnerable. Other synonyms might include dainty, wispy, feeble, effete, and weak. Depending on the context in which the word is being used, there may be other synonyms that could be more appropriate. Ultimately, the choice of synonym will depend on the intended meaning and the specific connotations that the word carries within the given context.