The present participle of a variant form of corroborate; confirming or supporting something in ongoing action.
From 'corroborate' with the gerund suffix '-ing,' possibly influenced by Australian English where 'corroboree' is a common word, creating confusion between the two similar words.
This word might be a confusion between 'corroborate' (to confirm) and 'corroboree' (Aboriginal celebration), showing how similar-sounding words can accidentally blend together in language when written down.
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