Ineffectual

google

ref

late Middle English: from medieval Latin ineffectualis, from in- ‘not’ + effectualis, from Latin effectus (see effect); in later use from in-1 ‘not’ + effectual.

wiktionary

ref

in- +‎  effectual

etymonline

ref

ineffectual (adj.)

early 15c., from in- (1) "not, opposite of" + effectual. Related: Ineffectually; ineffectuality.