Terrible head of department with study, almost packed (8)
I believe the answer is:
dreadful
'terrible' is the definition.
(I know that terrible can be written as dreadful)
'department with study almost packed' is the wordplay.
'department' becomes 'd' (abbreviation eg in MOD Ministry of Defence).
'with' is a charade indicator (letters next to each other).
'study' becomes 'read' (synonyms).
'almost' means to remove the last letter (almost the whole word is kept).
'packed' becomes 'full' (synonyms).
'full' with its final letter taken off is 'ful'.
'd'+'read'+'ful'='DREADFUL'
'head of' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for dreadful that I've seen before include "Atrocious, awful" , "Appalling, awful" , "Dire, alarming" , "Informally very bad, perhaps the weather" , "Horrible, shocking" .)