Fruit stone containing air and element of water (8)
I believe the answer is:
pimiento
'water' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'fruit stone containing air and element of' is the wordplay.
'fruit stone' becomes 'pit' (I've seen this in another clue).
'containing' means one lot of letters goes inside another.
'air' becomes 'mien' (I've seen this in another clue).
'and' means one lot of letters go next to another.
'element of' becomes 'o' (I can't justify this - if you can you should believe this answer much more).
'pit' going around 'mien' is 'pimient'.
'pimient'+'o'='PIMIENTO'
Can you help me to learn more?
(Other definitions for pimiento that I've seen before include "Sweet red capsicum" , "Allspice" , "Kitchen ingredient" , "Red sweet pepper" , "What's sweet yet spicy" .)