1) to mourn, weep, lament
1a) weeping as the sign of pain and grief for the thing signified (i.e. for the pain and grief)
1b) of those who mourn for the dead
2) to weep for, mourn for, bewail, one
Part of Speech: verb
Citing in TDNT: 3:722, 436
Of uncertain affinity; to sob, that is, wail aloud (whereas G1145 is rather to cry silently): - bewail. weep.
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 κλαίω; click on the second column to search for that grammatical form of the root κλαίω; click on the third column to search for that word and grammatical form; click on the total to search for the root κλαίω.