different between unconvincing vs ineffectual

English

un- +? convincing

unconvincing (comparative more unconvincing, superlative most unconvincing)

not convincing, plausible or believable
He gave me an unconvincing explanation of the fault, but I have my doubts.

unconvincing

in- +? effectual

ineffectual (comparative more ineffectual, superlative most ineffectual)

Unable or insufficient to produce effect.
Synonyms: futile; see also Thesaurus:futile
- 1865, Henry David Thoreau, Cape Cod, Chapter II. "Stage-coach Views", page 16.
  This coach was an exceedingly narrow one, but as there was a slight spherical excess over two on a seat, the driver waited till nine passengers had got in, without taking the measure of any of them, and then shut the door after two or three ineffectual slams, as if the fault were all in the hinges or the latch,—while we timed our inspirations and expirations so as to assist him.
Worthless.
Weak, indecisive; lacking forcefulness.

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