1) any visible object for preserving or recalling the memory of any person or thing
1a) a memorial, monument, specifically, a sepulchral monument
2) a sepulchre, a tomb
Part of Speech: noun neuter
Citing in TDNT: 4:680, 596
From G3420; a remembrance, that is, cenotaph (place of interment): - grave, sepulchre, tomb.
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 μνημεῖον; click on the second column to search for that grammatical form of the root μνημεῖον; click on the third column to search for that word and grammatical form; click on the total to search for the root μνημεῖον.