Pretty big facial hair covering sick up (7)
I believe the answer is:
tallish
'pretty big facial' is the definition.
Although both the answer and definition are adjectives, I cannot see how they can define each other.
'hair covering sick up' is the wordplay.
'hair' becomes 'tash' (I have seen 'Facial hair' mean 'tash' so perhaps 'hair' could also mean 'tash').
'covering' means one lot of letters goes inside another.
'sick' becomes 'ill' (synonyms).
'up' is a reversal indicator (in down clue: letters go upwards).
'ill' in reverse letter order is 'lli'.
'tash' going around 'lli' is 'TALLISH'.
Can you help me to learn more?
(Other definitions for tallish that I've seen before include "rather large" , "Consider" , "Rather lofty" .)