Feckless is an adjective to describe something that is worthless or irresponsible. Its root, feck, comes from the Scottish word for effect. So feckless could be thought of as something or someone that is without effect.
It also can be used as a noun or adverb, fecklessness and fecklessly, however, use in this forms is not common.
Examples
A new book claims that former Secretary of State and potential presidential hopeful Hillary Clinton called President Barack Obama “incompetent and feckless.” [CNBC]
Drawing on contemporary data, Edwards shows that claims of feckless complacency during the boom are greatly exaggerated. [Australian]
In fact, he took the stage during yesterday’s Order of Business to lambast these feckless birds for being mean and nasty to the locals and apparently they have even resorted to “stealing children’s lollipops.” [Independent Irish]
Nick’s wholly measured inward seething at the fecklessness of mankind, paired with Margaret’s steely can-do panache make a comforting vision of Britain being Great. [Independent UK]
In that sense, Abbott might as well be playing in the charade, denouncing Palmer’s fecklessness, irresponsibility and habit of being all things at once to all people. [Sydney Morning Herald]
In New York, construction workers punch out peaceniks; hippies, fecklessly self-absorbed, litter the parks. [New York Times]