Fairy left in danger (5)
I believe the answer is:
peril
'in danger' is the definition.
(I've seen this before)
'fairy left' is the wordplay.
'fairy' becomes 'peri' (Persian mythological being).
'left' becomes 'l' (common abbreviation).
'peri'+'l'='PERIL'
(Other definitions for peril that I've seen before include "Danger of serious kind" , "Hazardous situation" , "Danger, jeopardy" , "Exposure to harm" , "Immediate danger" .)