msspell3.dll is a module that contains functions for checking the spelling of a document file. The file comes with Word 6.0 for Windows.
Non-system processes like msspell3.dll originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues.