shortly vs in short

shortly and in short both are adverbs.

Word	Noun	Adjective	Verb	Adverb
shortly	No	No	No	Yes
in short	No	No	No	Yes

As adverbs, shortly and in short are synonyms defined as:

Other synonyms of shortly include briefly, concisely, in brief.

shortly (adverb)	in short (adverb)
in the near future	in a concise manner; in a few words
for a short time
in a curt, abrupt and discourteous manner
at a short distance
in a concise manner; in a few words