1) first in time or place
1a) in any succession of things or persons
2) first in rank
2a) influence, honour
3) first, at the first
Part of Speech: adverb
Citing in TDNT: 6:868, 965
Neuter of G4413 as an adverb (with or without G3588); firstly (in time, place, order, or importance): - before, at the beginning, chiefly, (at, at the) first (of all).
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 πρῶτον; click on the second column to search for that grammatical form of the root πρῶτον; click on the third column to search for that word and grammatical form; click on the total to search for the root πρῶτον.