When it comes to the term "subclassable", there are several alternatives that can be used to convey a similar meaning. "Inheritable" is a common synonym, implying that a class can be extended or passed down. Similarly, the term "extendable" is used to describe a class or object that can be expanded or built upon. "Derivable" is another suitable synonym, suggesting that a class can be derived or obtained from another. Moreover, the word "modifiable" indicates that a class can be changed or altered, capturing the essence of subclassing. In essence, these synonyms emphasize the notion of extending or building upon a class, thus offering flexibility in software development.