Scottish island dismissing one elder? (4)
I believe the answer is:
tree
'elder?' is the definition.
(elder is a kind of tree)
'scottish island dismissing one' is the wordplay.
'scottish island' becomes 'tiree' (island of the Inner Hebrides).
'dismissing' suggests deleting specific letters.
'one' becomes 'i' (Roman numeral).
'tiree' with 'i' removed is 'TREE'.
(Other definitions for tree that I've seen before include "Box or bay maybe?" , "eg Lime" , "''I think that I shall never see / A poem lovely as a ...'' (Kilmer)" , "Eg, laburnum" , "Genealogy chart" .)