1) to corrupt, to destroy
1a) in the opinion of the Jews, the temple was corrupted or "destroyed" when anyone defiled or in the slightest degree damaged anything in it, or if its guardians neglected their duties
1b) to lead away a Christian church from that state of knowledge and holiness in which it ought to abide
1c) to be destroyed, to perish
1d) in an ethical sense, to corrupt, deprave
Part of Speech: verb
Citing in TDNT: 9:93, 1259
Probably strengthened from φθίω phthiô (to pine or waste): properly to shrivel or wither, that is, to spoil (by any process) or (genitive) to ruin (especially figuratively by moral influences, to deprave): - corrupt (self), defile, destroy.
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 φθείρω; click on the second column to search for that grammatical form of the root φθείρω; click on the third column to search for that word and grammatical form; click on the total to search for the root φθείρω.