Rocket launch (5-3)
(Other definitions for liftoff that I've seen before include "Start of rocket's journey" , "flying start" , "Moment of launch" .)
'rocket launch' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lift-off that I've seen before include "Launch (of rocket)" , "Moment of rocket's launch" , "Instant when rocket leaves launching pad" , "Start of rocket's journey" .)
'rocket launch' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for blast-off that I've seen before include "First moment of a space mission" , "Rocket launch" , "The launching of a spacecraft - sounds explosive" , "Conclusion of countdown?" , "Start of a rocket's journey" .)