1) a mill stone
1a) a large mill consisted of two stones, an upper and an under one
1b) the "nether" stone was stationary, but the upper one was turned by an ass
2) a mill, the noise made by a mill
Part of Speech: noun masculine
Probably ultimately from the base of G3433 (through the idea of hardship); a "mill", that is, (by implication) a grinder (millstone): - millstone.
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 μύλος; click on the second column to search for that grammatical form of the root μύλος; click on the third column to search for that word and grammatical form; click on the total to search for the root μύλος.