Require shape-shifting alien to hide truth, initially (6)
I believe the answer is:
entail
'require shape' is the definition.
'entail' can be an answer for 'require' (I've seen this in another clue). I'm unsure of the 'shape' bit.
'shifting alien to hide truth initially' is the wordplay.
'shifting' indicates anagramming the letters.
'to hide' is an insertion indicator.
'initially' says to take the initial letters.
The initial letter of 'truth' is 't'.
'alien' anagrammed gives 'enail'.
'enail' placed around 't' is 'ENTAIL'.
Can you help me to learn more?
(Other definitions for entail that I've seen before include "Cause" , "legal restriction" , "Involve or require" , "outmoded fashion" , "Restriction on inheritance" .)