Bertha, bewitching in a bikini (6)
I believe the answer is:
'a bikini' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.
'bertha bewitching' is the wordplay.
'bertha' anagrams to 'BATHER'.
However, I am not clear how the anagram is indicated.
'in' is the link.
Can you help me to learn more?
(Other definitions for bather that I've seen before include "One dipping in the briny?" , "man getting soaked?" , "Seaside swimmer" , "one getting into the drink" .)