Badly regarded at first, but collecting tithes regularly (8)

I believe the answer is:

rottenly

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'badly' is the definition.
Both the definition and answer are adverbs. Perhaps they are linked in a way I don't understand?

'regarded at first but collecting tithes regularly' is the wordplay.
'at first' indicates taking the first letters.
'but' becomes 'only' (I've seen this in another clue).
'collecting' indicates putting letters inside.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The initial letter of 'regarded' is 'r'.
The alternate letters of 'tithes' are 'tte'.
'only' going around 'tte' is 'ottenly'.
'r'+'ottenly'='ROTTENLY'

Can you help me to learn more?

I've seen this clue in The Times.

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