classified ad vs classified advertisement

classified ad and classified advertisement both are nouns.

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

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

classified ad and classified advertisement: 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 ad include classified.

classified ad (noun)	classified advertisement (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