Monotony of psychic losing head after time (6)
I believe the answer is:
tedium
'monotony' is the definition.
(thesaurus)
'psychic losing head after time' is the wordplay.
'psychic' becomes 'medium' (medium is a kind of psychic).
'losing head' means to remove the first letter.
'after' is a charade indicator (letters next to each other).
'time' becomes 't'.
'medium' with its initial letter taken away is 'edium'.
'edium' put after 't' is 'TEDIUM'.
'of' acts as a link.
(Other definitions for tedium that I've seen before include "Boredom, mental weariness" , "'Boredom, ennui (6)'" , "Dullness, monotony" , "Banality" , "State of being bored" .)