Unpleasant new head coming to stay, perhaps (5)
I believe the answer is:
nasty
'unpleasant' is the definition.
(nasty can mean unpleasant or horrible)
'new head coming to stay perhaps' is the wordplay.
'head' says to take the initial letters.
'coming to' means one lot of letters go next to another.
'perhaps' indicates anagramming the letters.
The first letter of 'new' is 'n'.
'stay' is an anagram of 'asty'.
'n'+'asty'='NASTY'
(Other definitions for nasty that I've seen before include "Highly repugnant" , "Spiteful and unkind" , "Horrid, repugnant" , "Horrible" , "Not nice" .)