I almost stand for flag (4)
I believe the answer is:
iris
'for flag' is the definition.
(type of iris flower)
'i almost stand' is the wordplay.
'almost' becomes 'sir' (I can't explain this - if you can you should give a lot more credence to this answer).
'stand' is a reversal indicator (I've seen 'standing' mean this (in a down clue, letters stand up)).
'sir' in reverse letter order is 'ris'.
'i'+'ris'='IRIS'
Can you help me to learn more?
(Other definitions for iris that I've seen before include "Bright flower or eye part" , "Garden flower - part of eye" , "Flower and eye membrane" , "Coloured eye part" , "Film about writer _______ Murdoch" .)