1) a rock, cliff or ledge
1a) a projecting rock, crag, rocky ground
1b) a rock, a large stone
1c) metaphorically a man like a rock, by reason of his firmness and strength of soul
Part of Speech: noun feminine
Citing in TDNT: 6:95, 834
Feminine of the same as G4074; a (mass of) rock (literally or figuratively): - rock.
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 πέτρα; click on the second column to search for that grammatical form of the root πέτρα; click on the third column to search for that word and grammatical form; click on the total to search for the root πέτρα.