twenty-eighth vs 28th

twenty-eighth and 28th both are adjectives.

Word	Noun	Adjective	Verb	Adverb
twenty-eighth	No	Yes	No	No
28th	No	Yes	No	No

As adjectives, twenty-eighth and 28th are synonyms defined as:

twenty-eighth and 28th: coming next after the twenty-seventh in position

twenty-eighth (adjective)	28th (adjective)
coming next after the twenty-seventh in position	coming next after the twenty-seventh in position