Rich lass upset about unknown insect developing (9)

I believe the answer is:

chrysalis

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'insect developing' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.

'rich lass upset about unknown' is the wordplay.
'upset' is an anagram indicator.
'about' means one lot of letters goes inside another.
'unknown' becomes 'y' (algebra).
'rich'+'lass'='richlass'
'richlass' anagrammed gives 'chrsalis'.
'chrsalis' placed around 'y' is 'CHRYSALIS'.

Can you help me to learn more?

(Other definitions for chrysalis that I've seen before include "Old record company" , "insect developing" , "Pre-butterfly stage" , "Dormant insect pupa" , "Cocooned pupa of a moth or butterfly" .)

I've seen this clue in The Sun.

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