Home › Words › U › underspeedunderspeedunderspeed means an excessively-low speed; a speed lower than the minimum operating speed.Among words judged in Lexicurio's Arena, underspeed ranks #16,750 of 42,762 for Qualifying.EtymologyFrom under- + speed.nounAn excessively-low speed; a speed lower than the minimum operating speed.e.g.“An underspeed switch drops the load off if engine speed falls to 380 r.p.m. and an overspeed governor shuts the engine off if its speed rises above 1,700 r.p.m.” — 1961 August, “The English Electric Type 5 3,300 h.p. "Deltic" diesels for British Railways”, in Trains Illustrated, page 469:Definitions & examples from Wiktionary (CC BY-SA 3.0).