in fashion vs fashionable

in fashion and fashionable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
in fashion	No	Yes	No	No
fashionable	No	Yes	No	No

As adjectives, in fashion and fashionable are synonyms defined as:

in fashion and fashionable: popular and considered appealing or fashionable at the time

in fashion (adjective)	fashionable (adjective)
popular and considered appealing or fashionable at the time	being or in accordance with current social fashions
	having elegance or taste or refinement in manners or dress
	popular and considered appealing or fashionable at the time