Sentence:  <WSD>Traits</WSD> are parametrized on other methods, which must be provided to create a class using the <WSD>trait</WSD>. Using a <WSD>trait</WSD>-like mechanism to compose large collections of mutually-dependent classes or <WSD>traits</WSD> could lead to parameter explosion. 
Meaning of the word marked with <WSD> tags:  An uninstantiable collection of methods that provides functionality to a class by using the class's own interface.