head of steam

== English == === Etymology === The figurative sense is by metaphor from the literal one: the need of the boiler of a steam locomotive to exceed a minimum amount of pressure before the locomotive could start moving. === Pronunciation === === Noun === head of steam (plural heads of steam) (idiomatic) A significant amount of energy, vigour or momentum, sufficient to make progress or succeed in a task. Used other than figuratively or idiomatically: see head,‎ steam. ==== Related terms ==== ==== Translations ====