ready-to-wear vs off-the-rack

ready-to-wear is a noun but off-the-rack is not a noun.

Word	Noun	Adjective	Verb	Adverb
ready-to-wear	Yes	Yes	No	No
off-the-rack	No	Yes	No	No

As adjectives, ready-to-wear and off-the-rack are synonyms defined as:

ready-to-wear and off-the-rack: (especially of clothing) made in standard sizes and available from merchandise in stock

Other synonyms of ready-to-wear include off-the-peg, off-the-shelf.

ready-to-wear (noun)	off-the-rack (noun)
ready-made clothing

ready-to-wear (adjective)	off-the-rack (adjective)
(especially of clothing) made in standard sizes and available from merchandise in stock	(especially of clothing) made in standard sizes and available from merchandise in stock