1) to put together with, to place together, to join together
1a) to place in one's mind
1a1) to resolve, determine
1a2) to make an arrangement, to engage
1b) to assent to, to agree to
Part of Speech: verb
Middle voice from G4862 and G5087; to place jointly, that is, (figuratively) to consent (bargain, stipulate), concur: - agree assent, covenant.
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 συντίθεμαι; click on the second column to search for that grammatical form of the root συντίθεμαι; click on the third column to search for that word and grammatical form; click on the total to search for the root συντίθεμαι.