Moppet relied on becoming little bird (6)
I believe the answer is:
petrel
'bird' is the definition.
(petrel is a kind of bird)
'moppet relied on becoming little' is the wordplay.
'PETREL' is hidden in amongst the letters.
However, I'm unsure how this is indicated.
Can you help me to learn more?
(Other definitions for petrel that I've seen before include "18's [BIRD]" , "Seabird that flies far from land" , "Bird that sounds like fuel" , "Seabird sounds like fuel" , "Small seabird" .)