Join during emergency (5)
I believe the answer is:
merge
'join' is the definition.
(I've seen this before)
'during emergency' is the wordplay.
'during' says the answer is hidden in the clue.
'MERGE' is hidden in the letters of 'emergency'.
(Other definitions for merge that I've seen before include "Combine, coalesce" , "Combine, blend" , "Make one" , "Combine into one" , "Combine elements" .)