Transitive copying - plagiarism?
Your question sounds like you're asking about a math paper.  Definitions in mathematics are a bit of a strange corner case for plagiarism issues because they're not supposed to be "in your own words."  My understanding of normal behavior is that you would never put a definition in quotes (unless you're writing about history), that you can nonetheless reuse definitions verbatim, but that you need to either cite the original source or say that they are standard definitions.  A typical way to do this would be by saying "We recall some key definitions from X."