Like island with a large landmass (4)
I believe the answer is:
asia
'large landmass' is the definition.
(continent)
'like island with a' is the wordplay.
'like' becomes 'as'.
'island' becomes 'i' (geographical abbreviation).
'with' says to put letters next to each other.
'as'+'i'+'a'='ASIA'
(Other definitions for asia that I've seen before include "Continent bordering three oceans" , "Populous continent" , "Heavily populated area" , "Large continent" , "huge amount of ground" .)