Lacking courage, I’m one hiding in study regularly (5)
I believe the answer is:
timid
'lacking courage' is the definition.
(I've seen this before)
'i'm one hiding in study regularly' is the wordplay.
'one' becomes 'i' (Roman numeral).
'hiding in' means one lot of letters goes inside another.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'study' are 'td'.
'im'+'i'='imi'
'imi' going inside 'td' is 'TIMID'.
(Other definitions for timid that I've seen before include "Shrinking" , "Not brave" , "Lacking self-confidence" , "doormat" , "not forward" .)