ineffectual vs unable

ineffectual and unable both are adjectives.

Word	Noun	Adjective	Verb	Adverb
ineffectual	No	Yes	No	No
unable	No	Yes	No	No

As adjectives, ineffectual and unable are synonyms defined as:

Other synonyms of ineffectual include ineffective.

ineffectual (adjective)	unable (adjective)
not producing an intended effect	(usually followed by `to') not having the necessary means or skill or know-how
lacking in power or forcefulness	lacking in power or forcefulness
producing no result or effect	(usually followed by `to') lacking necessary physical or mental ability