1) to rejoice together with (another or others)
2) in the NT once to rejoice or delight with one's self or inwardly
Part of Speech: verb
Middle voice from G4862 and the base of G2237; to rejoice in with oneself, that is, feel satisfaction concerning: - delight.
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 συνήδομαι; click on the second column to search for that grammatical form of the root συνήδομαι; click on the third column to search for that word and grammatical form; click on the total to search for the root συνήδομαι.