Returning US soldier and you said an open aperture has a big lizard (6)
I believe the answer is:
iguana
'a big lizard' is the definition.
(I've seen this in another clue)
'returning us soldier and you said an open aperture' is the wordplay.
'returning' says the letters should be written backwards.
'us soldier' becomes 'GI' (informal term for a US soldier).
'and' means one lot of letters go next to another.
'said' shows a homophone (sound like).
'an open aperture' becomes 'ana' (I can't explain this - if you can you should give a lot more credence to this answer).
'you' sounds like 'u'.
'gi' in reverse letter order is 'ig'.
'ig'+'u'+'ana'='IGUANA'
'has' is the link.
Can you help me to learn more?
(Other definitions for iguana that I've seen before include "Tropical tree-lizard" , "Lizard Darwin found in the Galapagos" , "American lizard with a spiny crested back" , "reptile" , "Creature" .)