A Zulu in severe danger (6)
I believe the answer is:
hazard
'danger' is the definition.
(hazard is a kind of danger)
'a zulu in severe' is the wordplay.
'zulu' becomes 'z' (phonetic alphabet: alpha, bravo, charlie etc.).
'in' means one lot of letters goes inside another.
'severe' becomes 'hard' ('hard' can be a synonym of 'severe').
'a'+'z'='az'
'az' put into 'hard' is 'HAZARD'.
(Other definitions for hazard that I've seen before include "Possible source of danger" , "Risk; guess" , "Obstruction feature on a golf course" , "Jeopardy as on golf course" , "Golf course obstacle" .)