Is dictionary a common or proper noun?

No, the Word dictionary is a common noun; a Word for any dictionary of any kind.

A proper noun is the name of a person, a place, a thing, or a title; for example:

• Dictionary Hill, La Presa, CA
• Cambridge University Press Dictionary
• Merriam-Webster Collegiate Dictionary
• Oxford English Dictionary
• "The Sleeping Dictionary" 2003 movie starring Jessica Alba