Oyster? Simple to swallow half of it (6)
I believe the answer is:
native
'oyster?' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'simple to swallow half of it' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is located in the answer.
'simple' could be 'naive' (similar in meaning) and 'naive' is present in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for native that I've seen before include "Belonging to a particular place by birth" , "One who belongs to place by birth" , "One born in a certain place" , "mother" , "Endemic - aborigine" .)