Ship in a new Tesla key (9)
I believe the answer is:
important
'key' is the definition.
(I know that key can be written as important)
'ship in a new tesla' is the wordplay.
'ship in' becomes 'import' (to ship something in is to import it by ship).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'tesla' becomes 'T' (scientific unit).
'import'+'a'+'n'+'t'='IMPORTANT'
(Other definitions for important that I've seen before include "of great concern" , "It's vital" , "Main" , "Of significance or value" , "essence" .)