Noun: 1. The variety of fuel described in definition 4 above (from Hammond B-3, Oct 30, 2003, in case the numbers have changed). 2. A vehicle, including a railroad train, that runs on diesel (fuel). Adj.: Being or running on diesel (fuel).
The diesel runs on diesel--diesel fuel, you dig? (Not that you'd likely SAY that, but it does illustrate the meanings.)