Losing head, catty and restless (5)
I believe the answer is:
itchy
'restless' is the definition.
(synonyms)
'losing head catty' is the wordplay.
'losing head' means to remove the first letter.
'catty' becomes 'bitchy' (synonyms).
'bitchy' with its first letter taken off is 'ITCHY'.
'and' is the link.
(Other definitions for itchy that I've seen before include "Scratchy" , "Tickling" , "Have . . . . . feet - be restless, want to travel" , "Affected by desire" , "Like the feet of the restless" .)