Shy about beginning to participate in reproduction (4)
I believe the answer is:
copy
'reproduction' is the definition.
(I've seen this before)
'shy about beginning to participate' is the wordplay.
'shy' becomes 'coy' (coy can mean shy or modest).
'about' indicates putting letters inside.
'beginning to' says to take the initial letters.
The initial letter of 'participate' is 'p'.
'coy' going around 'p' is 'COPY'.
'in' is the link.
(Other definitions for copy that I've seen before include "written for paper" , "Unoriginal" , "Fake" , "Replicate" , "Imitation; matter to be printed" .)