1) to take up together with another or others
2) to bring together with others
2a) to cast up or settle accounts
2b) to make a reckoning with
Part of Speech: verb
From G4862 and G142; to make up together, that is, (figuratively) to compute (an account): - reckon, take.
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 συναίρω; click on the second column to search for that grammatical form of the root συναίρω; click on the third column to search for that word and grammatical form; click on the total to search for the root συναίρω.