"feck" was 17-18C underworld slang for "to steal by deceit". It is thought to be related to both "fake" and "effect", oddly enough. Like a number of other words of that period, it survived in Dublin long after it disappeared in England.

In the first of these threads, someone (Frank McGrath?) referred to a line in "The Night before Larry was stretched" which, of course, is in jail slang ("Newgate cant"). The line is "..Mind not such trifles a feck...".

Where does "feckless" fit in to all this? Not sure...

Regards