Fantastic calibre in bed's amazing (13)

I believe the answer is:

indescribable

'fantastic' is the definition.
(both can mean marvellous)

'calibre in bed's amazing' is the wordplay.
'amazing' is an anagram indicator.
'calibre'+'in'+'beds'='calibreinbeds'
'calibreinbeds' with letters rearranged gives 'INDESCRIBABLE'.

(Another definition for indescribable that I've seen is " Defeating words".)

I've seen this clue in The Telegraph.

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