The term 'GIVE GAS TO AN ENGINE' can be summarized as providing fuel to a motor. The crossword solution for this term is REV, which is an abbreviation for the verb 'revving', which is the act of increasing the speed of an engine by pressing the accelerator. Revving an engine requires fuel, and thus the term 'GIVE GAS TO AN ENGINE' is referring to providing fuel to the engine in order to increase its speed.