Crestfallen or tickled about discovering oil? (10)

I believe the answer is:

citronella

I'm a little stuck... Click here to teach me more about this clue!

'oil?' is the definition.
Both the answer and definition are singular nouns.
Maybe there's an association between them I don't understand?

'crestfallen or tickled about discovering' is the wordplay.
'discovering' indicates a hidden word (I've seen 'discovered' mean this (remove the letters covering the answer in the clue)).
'about' is a reversal indicator.
'allenortic' can be found hidden inside 'crestfallen or tickled'.
'allenortic' back-to-front is 'CITRONELLA'.

Can you help me to learn more?

(Other definitions for citronella that I've seen before include "South Asian grass" , "Insect-repelling oil" .)

I've seen this clue in The Independent.

Want a hint initially instead of a full solution? Install my app