Poisonous substance eroded half my ground (12)

I believe the answer is:

formaldehyde

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'poisonous substance' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'eroded half my ground' is the wordplay.
'ground' indicates an anagram ('grind' the letters into a new form).
'eroded'+'half'+'my'='erodedhalfmy'
'erodedhalfmy' with letters rearranged gives 'FORMALDEHYDE'.

Can you help me to learn more?

(Other definitions for formaldehyde that I've seen before include "Creatures preserved here" , "Gas used as preservative" , "Preservative for biological specimens" .)

I've seen this clue in The Times.

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