Global promise to preserve life, primarily (5)
I believe the answer is:
world
'global' is the definition.
(I know that global can be written as world)
'promise to preserve life primarily' is the wordplay.
'promise' becomes 'word' (as in 'I give you my word').
'to preserve' means one lot of letters goes inside another.
'primarily' says to take the initial letters.
The first letter of 'life' is 'l'.
'word' going around 'l' is 'WORLD'.
(Other definitions for world that I've seen before include "Field" , "Annual US baseball championship games" , "Sphere of activity" , "Earth and its inhabitants" , "Cosmos" .)