Green’s Dictionary of Slang

strong, tough, muscular.

1995		L. Stavsky et al. A2Z.
1996		Eble Campus Sl. Sept.
1997–2001		Online Sl. Dict. 🌐 diesel adj 1. muscular. (‘Check out his body, he’s diesel.’).
2003		Eble Campus Sl. Nov. 2: diesel – very muscular: After three years of going to the gym, my brother is diesel.
2016		Twitter 27 May 🌐 There’s woman in #N7 (what we used to call ‘a real Diesel number’: is that still OK?) has *every inch* of her neck, face, skull tattoo’d.