One could say I sneer around model-types (6)
I believe the answer is:
letter
'one could say i' is the definition.
I can't tell whether this defines the answer.
'sneer around model-types' is the wordplay.
'sneer' becomes 'leer' (synonyms).
'around' means one lot of letters goes inside another.
'model' becomes 'T' (Ford Model T car).
'types' becomes 't' (this might be a standard abbreviation which I don't know about).
't'+'t'='tt'
'leer' enclosing 'tt' is 'LETTER'.
Can you help me to learn more?
(Other definitions for letter that I've seen before include "Item sent - character" , "Written note" , "A, B or C, for example" , "reference?" , "Written message" .)