Observe delta germ (4)
I believe the answer is:
seed
'germ' is the definition.
(I know that germ can be written as seed)
'observe delta' is the wordplay.
'observe' becomes 'see' (I've seen this in other clues).
'delta' becomes 'd' (phonetic alphabet: alpha, bravo, charlie etc.).
'see'+'d'='SEED'
(Other definitions for seed that I've seen before include "From which things grow" , "Local escorted" , "An outstanding player in a tournament" , "A plant grows from it" , "Initiate the growth of" .)