Core components in speedy prognostication (8)
I believe the answer is:
forecast
'prognostication' is the definition.
(thesaurus)
'core components in speedy' is the wordplay.
'components' indicates an anagram.
'in' is an insertion indicator.
'speedy' becomes 'fast' (similar in meaning).
'core' is an anagram of 'orec'.
'orec' inserted inside 'fast' is 'FORECAST'.
(Other definitions for forecast that I've seen before include "tip" , "Expect" , "Predict (event)" , "Predict as with weather" , "Prediction, about the weather perhaps" .)