Mil is also a term for one tenth of a cent (or one thousandth of a dollar) in U.S. currency. Often seen on ballots, where a certain referendum might ask for a couple of mils per dollar of taxes for some worthy cause. Webster says that this is spelled mill, but common usage seems to be divided evenly between the two spellings.

Mil can also mean :

• One million dollars (colloquial)
• .mil is also one of the top level domains for internet names : see RFC 1956 (Registration in the MIL Domain).
• Thousand in the context of "particles found at a density of 37.5 per mil".
• A monetary unit formerly used in Cyprus equal to 1/1000 pound. (Currently Cyprus uses Cyprus Pounds or CYP)
• A unit of angular measurement equal to 1/6400 of 360 degrees and used especially in artillery (that's 9/160 degrees or 0.05625 degrees or 3 minutes and 22.5 seconds)
• As ModernAngel said, 1/1000th of 1 inch. Human hair is about 3 mils thick. Industrial laminates (such as laminated cable shield) may be composed of foil and plastic only tenths of a mil in thickness.
• Short for Mother-In-Law, according to dem bones.