Dad’s way is old-fashioned (5)

I believe the answer is:

passe

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

'old-fashioned' is the definition.
(synonyms)

'dad's way' is the wordplay.
'dad' becomes 'pa' (synonyms).
'way' becomes 'sse' (I can't explain this - if you can you should believe this answer much more).
'pa'+'sse'='PASSE'

'is' is the link.

Can you help me to learn more?

(Other definitions for passe that I've seen before include "dated" , "Old hat" , "Outdated" , "Past its prime - in France" , "-- -partout" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app