See 'The Sixth Sense' on YouTube initially (4)
I believe the answer is:
espy
'see' is the definition.
(thesaurus)
'the sixth sense on youtube initially' is the wordplay.
'the sixth sense' becomes 'esp' (I've seen this in other clues).
'on' says to put letters next to each other.
'initially' suggests taking the first letters.
The initial letter of 'youtube' is 'y'.
'esp'+'y'='ESPY'
(Other definitions for espy that I've seen before include "Watch" , "Spot; observe" , "Catch a glimpse of" , "Perceive" , "Behold" .)