1) a pricking, piercing
2) severe sorrow, extreme grief
3) insensibility or torpor of mind, such as extreme grief easily produces
3a) hence a "spirit of stupor", which renders their souls torpid so insensible that they are not affected at all by the offer made them of salvation through the Messiah
Part of Speech: noun feminine
Citing in TDNT: 3:626, 419
From G2660; a prickling (sensation, as of the limbs asleep), that is, (by implication [perhaps by some confusion with G3506 or even with G3571]) stupor (lethargy): - slumber.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root κατάνυξις; click on the second column to search for that grammatical form of the root κατάνυξις; click on the third column to search for that word and grammatical form; click on the total to search for the root κατάνυξις.