Hairstyle the prevailing fashion certainly (7)

I believe the answer is:

tonsure

I'm a little stuck... Click here to teach me more about this clue!

'hairstyle' is the definition.
(hairstyle used by monks)

'prevailing fashion certainly' is the wordplay.
'prevailing fashion' becomes 'ton' (I've seen this before. I am not sure about the 'prevailing' bit.).
'certainly' becomes 'sure' (synonyms).
'ton'+'sure'='TONSURE'

'the' is the link.

Can you help me to learn more?

(Other definitions for tonsure that I've seen before include "Monastic hairstyle" , "Monastic haircut" , "Monk's hairdo" , "Shearing ?" , "Close-shaved hairstyle" .)

I've seen this clue in The Globe and Mail.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.