Mislay the ring in it that's too big (5)
I believe the answer is:
loose
'too big' is the definition.
I can't judge whether this definition defines the answer.
'mislay the ring in it' is the wordplay.
'mislay' becomes 'lose' (synonyms).
'the ring' becomes 'o' (letter resembling a ring).
'in it' means one lot of letters goes inside another.
'lose' enclosing 'o' is 'LOOSE'.
'that's' acts as a link.
Can you help me to learn more?
(Other definitions for loose that I've seen before include "Lax or at large" , "Untie; dissolute" , "Unfixed" , "Promiscuous" , "wobbly" .)