Feckless is a weird adjective that means “ineffective”, “futile”, “lazy”, or “indifferent”.

The Online Etymology Dictionary explains that it comes from the Scots word feck, a shortened version of effect, and it was “popularized by Carlyle, who left its opposite, feckful, in dial. obscurity”.

The word feck sounds a lot like a common expletive used in English (hint: it also starts with an “f” and ends with a “ck”). Well, according to Wikipedia’s page on feck, it actually is used that way in modern Irish English. It can also mean “to throw”, “to steal”, and more. Meanwhile, the English word feckless doesn’t seem to be nearly as common (or as interesting).