1) a diadem
1a) a blue band marked with white which Persian kings used to bind on the turban or tiara
1b) the kingly ornament for the head, the crown
Part of Speech: noun neuter
From a compound of G1223 and G1210; a "diadem" (as bound about the head): - crown. Compare G4735.
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 διάδημα; click on the second column to search for that grammatical form of the root διάδημα; click on the third column to search for that word and grammatical form; click on the total to search for the root διάδημα.