Intense as, say, Jack Palance's debut (4)
I believe the answer is:
deep
'intense' is the definition.
(associated in meaning)
'say jack palance's debut' is the wordplay.
'say jack' becomes 'Dee' (Jack Dee is a comedian).
'debut' suggests taking the first letters.
The first letter of 'palance' is 'p'.
'dee'+'p'='DEEP'
'as' acts as a link.
(Other definitions for deep that I've seen before include "Mysterious" , "down a long way" , "Profound - cunning - sea - bass" , "hard to understand" , "Sunk low" .)