A kind of dam incorporated by Sizewell (3)
I believe the answer is:
ewe
'a kind of dam' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Maybe there's an association between them I don't understand?
'incorporated by sizewell' is the wordplay.
'EWE' is hidden within the letters.
However, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for ewe that I've seen before include "Lamb's mother" , "Farm animal" , "A palindromic sheep" , "Lamb's dam" , "She'll provide material to knit" .)