1. underboost - Noun
2. underboost - Verb
underboost (third-person singular simple present underboosts, present participle underboosting, simple past and past participle underboosted)
To create too little pressure in an engine's combustion chamber.
(uncountable) The process of underboosting.
(countable) An instance of underboost.
Source: en.wiktionary.org