Hmm.. well i'm thinking that this phrase probably did have a mean once... and maybe somebody somewhere still knows what they line actually said... BUT Seeing as most all who were to sing the song was Drunk off their sorry bums... i'm sure whoever picked it up and brought it elsewhere than where it was from probably misunderstood the slurrs.. of the irish or english or british or whoevers drunkin soul was singing the song.. My question is why do they sya Whack?? See here is the chorus :    Musha ringum duram da
            whack! for the laddie-O
            whack! for the laddie-O
          there's whiskey in the jar

And another question how is it sung? the tune i mean..