It can be worn with a worried air by a school head (4)
I believe the answer is:
sari
'it can be worn' is the definition.
The definition suggests a singular noun which matches the answer.
'worried air by a school head' is the wordplay.
'worried' indicates an anagram (worry can mean to interfere with or disturb).
'by' is a charade indicator (letters next to each other).
'head' indicates taking the first letters.
The initial letter of 'school' is 's'.
'air' with letters rearranged gives 'ari'.
'ari' after 's' is 'SARI'.
'with a' acts as a link.
Can you help me to learn more?
(Other definitions for sari that I've seen before include "Traditional dress of Hindu women" , "Asian dress" , "Traditional Indian garment" , "Traditional Indian women's dress" , "Traditional dress of Indian women" .)