Very, very angry losing head — that's clear (5)
I believe the answer is:
vivid
'clear' is the definition.
('vivid' can be similar in meaning to 'clear')
'very very angry losing head' is the wordplay.
'very' becomes 'v' (abbreviation).
'very angry' becomes 'livid' (I've seen this before).
'losing head' means to remove the first letter.
'livid' with its initial letter taken away is 'ivid'.
'v'+'ivid'='VIVID'
'that's' is the link.
(Other definitions for vivid that I've seen before include "Intensely deep/bright" , "Lifelike, striking" , "Intensely striking in colour" , "Very bright and colourful" , "Graphic" .)