Plain girl one boy stood up – and another (9)
I believe the answer is:
unadorned
'plain' is the definition.
(similar in meaning)
'girl one boy stood up and another' is the wordplay.
I cannot quite see how this works, but
'girl' could be 'adorne' and 'adorne' is present in the answer.
'one' could be 'un' (northern English dialect form of 'one') and 'un' is located in the answer.
A single letter 'd' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for unadorned that I've seen before include "Plain, undecorated" , "Simple and plain as around den" , "Not decorated, plain and simple" , "Without embellishment" .)