Secured when not eating (4)
I believe the answer is:
fast
I believe this is a double definition.
'secured' is the first definition.
(synonyms)
'not eating' is the second definition.
(a fast is a period of not eating)
'when' is the link.
(Other definitions for fast that I've seen before include "'Quickly, rapidly (4)'" , "Starve; quick" , "Quick; firmly fixed" , "Don't scoff" , "Eat nothing" .)