Think about being complete after gender reassignment (4)
I believe the answer is:
mull
'think about' is the definition.
(thesaurus)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for mull that I've seen before include "Warm (wine) with spices; Scottish island" , "Reflect deeply on the Scottish headland" , "Heat wine with sugar and spice" , "Consider" , "Ponder; Scottish isle" .)