1) a seal
1a) the seal placed upon books
1b) a signet ring
1c) the inscription or impression made by a seal
1c1) of the name of God and Christ stamped upon their foreheads
1d) that by which anything is confirmed, proved, authenticated, as by a seal (a token or proof)
Part of Speech: noun feminine
Citing in TDNT: 7:939, 1127
Probably strengthened from G5420; a signet (as fencing in or protecting from misappropriation); by implication the stamp impressed (as a mark of privacy, or genuineness), literally or figuratively: - seal.
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 σφραγίς; click on the second column to search for that grammatical form of the root σφραγίς; click on the third column to search for that word and grammatical form; click on the total to search for the root σφραγίς.