Fly-by-night corrupt liar, new woman that made partner

I believe the answer is:

mother-in-law

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'woman that made partner' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see an association between them that I can't see?

'fly-by-night corrupt liar new' is the wordplay.
'fly-by-night' becomes 'moth' (I am not sure about this - if you are sure you should believe this answer much more).
'corrupt' is an anagram indicator.
'liar'+'new'='liarnew'
'liarnew' with letters rearranged gives 'erinlaw'.
'moth'+'erinlaw'='MOTHER-IN-LAW'

Can you help me to learn more?

(Other definitions for mother-in-law that I've seen before include "Relative - woman Hitler (anag)" , "Relative by marriage" .)

I've seen this clue in The Telegraph.

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