Our word of the week is vigliacco, "coward." The common adjective is vile ("cowardly," not "vile"- it's a false friend)(although cowards are vile). The abstract noun is vilta' ("cowardice") and a single act of cowardice is a vigliaccata.
A synonym, somewhat less common, is codardo. The abstract noun is codardia.
If you want to insult someone, vigliacco is better, as it has that nice, hard -acc sound that sounds like a reproof in itself.