Mistress last month put in clinic close to Chelsea (7)
I believe the answer is:
sultana
'mistress' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'last month put in clinic close to chelsea' is the wordplay.
'last month' becomes 'ult' (short for 'last month' in correspondence).
'put in' is an insertion indicator.
'clinic' becomes 'san' (short for sanatorium).
'close to' indicates one should take the final letters (the 'close' to the word).
The final letter of 'chelsea' is 'a'.
'ult' put inside 'san' is 'sultan'.
'sultan'+'a'='SULTANA'
Can you help me to learn more?
(Other definitions for sultana that I've seen before include "Shrivelled up" , "Small dried fruit" , "Dried fruit - woman in harem" , "bit of a fruit cake" , "Dried white grape" .)