So I don dey do the work of Dictionary!!!

OK na, but you go square o!! You know say egunje spoil Lagos

Odometer is the device which measure distance covered in your vehicle. The unit of measurement will be either metric (kilometer) or imperial (mile). In most cars you have at least 2 odometers. The first keep a record of all the distance covered from the manufacture of the car. This cannot be reset except by "SPECIAL" means.

The second one, also referde to as "trip meter" can be reset to indicate particular distances.
You are are talking or 2 things, the measureing instrument (odometer) and the measured parameter's unit (kilolmeter), Mileage is another word you might come across and this refers to the odometer reading in what ever unit that is measured.
I hope it helps.