Sockdolager \sok-DOL-uh-jer\ , noun;
1. A decisive reply, argument
2. Something unusually large, heavy, etc.
3. A heavy, finishing blow
This word dates to 1830 and the consensus seems to be that it's a fanciful formation, based on the verb sock meaning "hit hard". There is also a possibility that it is a variant on doxology, which is a short hymn of praise. The sense of "something exceptional" was first attested in 1838. Interestingly the word sockdologising was nearly the last word President Abraham Lincoln heard before being shot. As the story goes, John Wilkes Booth was very familiar with the play ("Our American Cousin" by Tom Taylor) so he waited for the line, "Well, I guess I know enough to turn you inside out, you sockdologising old man-trap," and when the audience laughed he shot.
Today's word and the first definition were both taken from Dictionary.com's 'Word of the Day' for Saturday, January 8
Etymologies come from the Oxford English Dictionary and/or Etymonline.com