1) laying bear, making naked
2) a disclosure of truth, instruction
2a) concerning things before unknown
2b) used of events by which things or states or persons hitherto withdrawn from view are made visible to all
3) manifestation, appearance
Part of Speech: noun feminine
Citing in TDNT: 3:563, 405
From G601; disclosure: - appearing, coming, lighten, manifestation, be revealed, revelation.
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 ἀποκάλυψις; click on the second column to search for that grammatical form of the root ἀποκάλυψις; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀποκάλυψις.