One stealing article I put inside, fearful initially (5)
I believe the answer is:
thief
'one stealing' is the definition.
(thieves steal things)
'article i put inside fearful initially' is the wordplay.
'article' becomes 'the' (the definite article in English).
'put inside' is an insertion indicator.
'initially' indicates taking the first letters.
The initial letter of 'fearful' is 'f'.
'the' enclosing 'i' is 'thie'.
'thie'+'f'='THIEF'
(Other definitions for thief that I've seen before include "One who steals" , "Unlawful taker" , "One with taking ways" , "Aus. or Scots city" , "Stealer" .)