Some prisoner, uptight, is to break out (5)
I believe the answer is:
erupt
'to break out' is the definition.
(synonyms)
'some prisoner uptight is' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'ERUPT' can be found hidden inside 'prisoner uptight is'.
(Other definitions for erupt that I've seen before include "Blow up like volcano" , "Burst forth violently" , "be active" , "Discharge" , "Burst forth, like 25" .)