Definition of "slug"
slug1
/slʌɡ/
noun
plural slugs
(rail transport) An accessory to a diesel-electric locomotive, used to increase adhesive weight and allow full power to be applied at a lower speed. It has trucks with traction motors, but lacks a prime mover, being powered by electricity from the mother locomotive, and may or may not have a control cab.
(US, slang, District of Columbia) A hitchhiking commuter.
(obsolete) A hindrance, an obstruction.
verb
third-person singular simple present slugs, present participle slugging, simple past and past participle slugged