I use Firefox on my iMac. I can't see how Safari would affect the spell checker on CC, but that might be beyond my expertise. If you really suspect Safari though, a reinstall might just help. Also, run Disk Utilities (Repair Disk Permissions) and reboot into Safe Boot by holding the Shift key down while starting up. This should repair and defrag System files. Once it is up and running, restart normally. That should speed up your machine too.