Like doctor on English ship to join outfit (5,5)
I believe the answer is:
fancy dress
'join outfit' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'like doctor on english ship' is the wordplay.
'like' becomes 'fancy' (both can mean to find someone attractive).
'doctor' becomes 'dr' (abbreviation).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'english' becomes 'E' (abbreviation).
'ship' becomes 'SS' (prefix in ship names eg SS Great Britain).
'fancy'+'dr'+'e'+'ss'='FANCY DRESS'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for fancy dress that I've seen before include "Themed party attire" , "Masquerade costume?" , "Party costume" , "Frivolous party garb" .)