Innocent tense in pursuit (6)
I believe the answer is:
chaste
'innocent' is the definition.
(I've seen this before)
'tense in pursuit' is the wordplay.
'tense' becomes 't' (abbreviation used in many dictionaries).
'in' means one lot of letters goes inside another.
'pursuit' becomes 'chase' (synonyms).
't' placed inside 'chase' is 'CHASTE'.
(Other definitions for chaste that I've seen before include "Modest and virtuous" , "Untarnished" , "Set Cha up for being pure" , "Decorous" , "Modest, pure" .)