1) it is necessary, there is need of, it behooves, is right and proper
1a) necessity lying in the nature of the case
1b) necessity brought on by circumstances or by the conduct of others toward us.
1c) necessity in reference to what is required to attain some end
1d) a necessity of law and command, of duty, equity
1e) necessity established by the counsel and decree of God, especially by that purpose of his which relates to the salvation of men by the intervention of Christ and which is disclosed in the Old Testament prophecies
1e1) concerning what Christ was destined finally to undergo, his sufferings, death, resurrection, ascension
Part of Speech: verb
Citing in TDNT: 2:21, 140
Third person singular active present of G1210; also δεόν deon which is neuter active participle of the same; both used impersonally; it is (was, etc.) necessary (as binding): - behoved, be meet, must (needs), (be) need (-ful), ought, should.
|a be necessary||71.34|
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 δεῖ; click on the second column to search for that grammatical form of the root δεῖ; click on the third column to search for that word and grammatical form; click on the total to search for the root δεῖ.