Being sixteen, suspect taking coke not OK (9)
I believe the answer is:
existence
'being' is the definition.
(synonyms)
'sixteen suspect taking coke not ok' is the wordplay.
'suspect' indicates an anagram (a suspicious or unusual spelling).
'taking' means one lot of letters go next to another.
'not' is a deletion indicator.
'coke' with 'ok' taken out is 'ce'.
'sixteen' with letters rearranged gives 'existen'.
'existen'+'ce'='EXISTENCE'
(Other definitions for existence that I've seen before include "State of being" , "A way of living" , "Way of life" , "survival" , "The business of being" .)