Coercion needed but you finally got into a frock! (6)
I believe the answer is:
duress
'coercion' is the definition.
(under duress means being coerced)
'you finally got into a frock' is the wordplay.
'finally' says to take the final letters.
'got into' is an insertion indicator.
'a frock' becomes 'dress' ('dress' can be a synonym of 'frock').
The last letter of 'you' is 'u'.
'u' going within 'dress' is 'DURESS'.
'needed but' acts as a link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for duress that I've seen before include "Constraint, coercion" , "The use of force or threats to get one's way" , "Constraint, Compulsion" , "Illegal coercion" , "Compulsion by use of force" .)