unable or insufficient to produce effect; futile (adjective)
weak; lacking forcefulness (adjective)
Examples of word ineffectual
Walter Bassett broke out in ineffectual protest, but was swiftly silenced by the threat of a lunacy commission.
Then when the Mexicans fired off a few rockets at us in ineffectual retaliation, with negligible damage to us, we would then have responded with a massive bombing campaign against Mexican civilian infrastructure, killing a hundred or more Mexicans to every one American killed.