Thin creature to remain in group (5,6)
I believe the answer is:
stick insect
'thin creature' is the definition.
'stick insect' can be an answer for 'creature' (stick insect is a kind of creature). I am not certain of the 'thin' bit.
'remain in group' is the wordplay.
'remain' becomes 'stick' (both can mean to stay).
'group' becomes 'sect' (I've seen this in other clues).
'stick'+'in'+'sect'='STICK-INSECT'
'to' is the link.
Can you help me to learn more?
(Other definitions for stick insect that I've seen before include "Its limbs look like twigs" , "Twiggy lookalike" , "Bug that's noted for camouflage" , "creature hard to spot in tree" , "Twig-like creature" .)