39th vs thirty-ninth

39th and thirty-ninth both are adjectives.

Word	Noun	Adjective	Verb	Adverb
39th	No	Yes	No	No
thirty-ninth	No	Yes	No	No

As adjectives, 39th and thirty-ninth are synonyms defined as:

39th and thirty-ninth: the ordinal number of thirty-nine in counting order

39th (adjective)	thirty-ninth (adjective)
the ordinal number of thirty-nine in counting order	the ordinal number of thirty-nine in counting order