1) top of the heap, the first fruits
1a) best of the spoils or crops
2) the Greeks customarily selected from the topmost part of the heaps and offered this to the gods
Part of Speech: noun neuter
From G206 and θίς this (a heap); properly (in the plural) the top of the heap, that is, (by implication) best of the booty: - spoils.
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 ἀκροθίνιον; click on the second column to search for that grammatical form of the root ἀκροθίνιον; click on the third column to search for that word and grammatical form; click on the total to search for the root ἀκροθίνιον.