Most of national flag (4)
I believe the answer is:
iris
'flag' is the definition.
(type of iris flower)
'most of national' is the wordplay.
'most of' means to remove the last letter.
'national' becomes 'Irish' (from Ireland).
'irish' with its final letter removed is 'IRIS'.
(Other definitions for iris that I've seen before include "Murdoch in writing" , "Circular coloured membrane in the eye" , "Film about writer _______ Murdoch" , "may open up in camera" , "Bright flower or eye part" .)