For certain and One and only

For certain adverb - Definitely or positively (`sure' is sometimes used informally for `surely').

One and only and for certain are semantically related. In some cases you can use "One and only" instead an adverb phrase "For certain".

One and only adjective - Eminent beyond or above comparison.

For certain and one and only are semantically related. Sometimes you can use "For certain" instead an adverb phrase "One and only".