Abba = "father"
1) father, customary title used of God in prayer. Whenever it occurs in the New Testament it has the Greek interpretation joined to it, that is apparently to be explained by the fact that the Chaldee "ABBA" through frequent use in prayer, gradually acquired the nature of a most sacred proper name, to which the Greek speaking Jews added the name from their own tongue.
Part of Speech: noun
Citing in TDNT: 1:5, 1
Of Chaldee origin [H2]; father (as a vocative): - Abba.
|Father (a title for God)||12.12|
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 αββα; click on the second column to search for that grammatical form of the root αββα; click on the third column to search for that word and grammatical form; click on the total to search for the root αββα.