permissible vs allowable

permissible and allowable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
permissible	No	Yes	No	No
allowable	No	Yes	No	No

As adjectives, permissible and allowable are synonyms defined as:

permissible and allowable: that may be permitted especially as according to rule

permissible (adjective)	allowable (adjective)
that may be permitted especially as according to rule	that may be permitted especially as according to rule
that may be accepted or conceded	deserving to be allowed or considered
	deductible according to the tax laws