Crossword Genius

Most fashionable tendency that's on the way (9)

Ross

I believe the answer is:

trendiest

'most fashionable' is the definition.
('trendy' can be similar in meaning to 'fashionable')

'tendency that's on the way' is the wordplay.
'tendency' becomes 'trend' (trend is a kind of tendency).
'that's' becomes 'ie'.
'on' is a charade indicator (letters next to each other).
'the way' becomes 'st' (abbreviation for street).
'trend'+'ie'+'st'='TRENDIEST'

(Other definitions for trendiest that I've seen before include "Most cool!" , "cooler than the rest" , "Most popular" .)

I've seen this clue in the Sydney Morning Herald.
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.