Peril, as close, dreadful portent in sky? (5,7)

I believe the answer is:

solar eclipse

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'portent in sky?' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'peril as close dreadful' is the wordplay.
'dreadful' is an anagram indicator.
'peril'+'as'+'close'='perilasclose'
'perilasclose' anagrammed gives 'SOLAR ECLIPSE'.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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