Silver mesh in second generator (7)
I believe the answer is:
magneto
'generator' is the definition.
(I know that magneto is a type of generator)
'silver mesh in second' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'mesh' becomes 'net' (synonyms).
'in' means one lot of letters goes inside another.
'second' becomes 'mo' (both are short periods of time).
'ag'+'net'='agnet'
'agnet' put inside 'mo' is 'MAGNETO'.
(Other definitions for magneto that I've seen before include "kindles a spark" , "Car generator" , "engine part" , "Ignition apparatus" , "Ignition device" .)