School head airs off dresses (5)
I believe the answer is:
saris
'dresses' is the definition.
(sari is a kind of dress)
'school head airs off' is the wordplay.
'head' suggests taking the first letters.
'off' is an anagram indicator.
The first letter of 'school' is 's'.
'airs' anagrammed gives 'aris'.
's'+'aris'='SARIS'
(Other definitions for saris that I've seen before include "Dresses worn primarily by Hindu women" , "Garments" .)