Excessively large plane? (4)
I believe the answer is:
tool
'plane?' is the definition.
(plane is a kind of tool)
'excessively large' is the wordplay.
'excessively' becomes 'too' (synonyms).
'large' becomes 'L' (eg in clothes sizes).
'too'+'l'='TOOL'
(Other definitions for tool that I've seen before include "Practical implement" , "organ" , "Weapon" , "Hand implement" , "Cat's-paw; impress design on" .)