'Zine on web covering oxygen generator (7)
I believe the answer is:
magneto
'generator' is the definition.
(I know that magneto is a type of generator)
''zine on web covering oxygen' is the wordplay.
''zine' becomes 'mag' (I've seen this in another clue).
'on' says to put letters next to each other.
'web' becomes 'net' (synonyms).
'covering' says to put letters next to each other (on top of in down clue).
'oxygen' becomes 'O' (atomic symbol for oxygen).
'mag'+'net'+'o'='MAGNETO'
(Other definitions for magneto that I've seen before include "generation device" , "kindles a spark" , "Ignition device" , "Small type of generator" , "Ignition apparatus" .)