Feckless
/ˈfɛkləs/
adjective
lacking initiative or strength of character; irresponsible
The word 'feckless' comes from the Scottish dialect word 'feck', meaning 'effect' or 'value'. So, 'feckless' literally means lacking value or effect, hence the idea of someone being ineffective or irresponsible.
See how George R. R. Martin, Stephen King and 2 other authors use "feckless", with its meaning, pronunciation and real book examples.
Examples from books
His eyes lost their menacing cast (they were bottlegreen, and how could such clear and feckless eyes have seemed menacing, or even dark?).
Stephen King
The Stand
Now look, this is our Caspar, feckless Caspar, returned from the Hague.
Gregory Maguire
Confessions of an Ugly Step Sister
Aeron Greyjoy had been the most amiable of his uncles, feckless and quick to laugh, fond of songs, ale, and women.
George R. R. Martin
A Clash of Kings
They were incorrigibly children of the idea, feckless and colour-blind, to whom body and spirit were forever and inevitably opposed.
T. E. Lawrence
Seven Pillars of Wisdom