classified advertisement vs classified ad

classified advertisement and classified ad both are nouns.

Word	Noun	Adjective	Verb	Adverb
classified advertisement	Yes	No	No	No
classified ad	Yes	No	No	No

As nouns, classified advertisement and classified ad are synonyms defined as:

classified advertisement and classified ad: a short ad in a newspaper or magazine (usually in small print) and appearing along with other ads of the same type

Other synonyms of classified advertisement include classified.

classified advertisement (noun)	classified ad (noun)
a short ad in a newspaper or magazine (usually in small print) and appearing along with other ads of the same type	a short ad in a newspaper or magazine (usually in small print) and appearing along with other ads of the same type