1a) what one can not do without, indispensable
1b) connected by bonds of nature or friendship
1c) what ought according to the law of duty be done, what is required by the circumstances
Part of Speech: adjective
Citing in TDNT: 1:344, 55
From G318; necessary; by implication close (of kin): - near, necessary, necessity, needful.
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 ἀναγκαῖος; click on the second column to search for that grammatical form of the root ἀναγκαῖος; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀναγκαῖος.