Suppressions about illumination on hills (10)

I believe the answer is:

clampdowns

I'm a little stuck... Click here to teach me more about this clue!

'suppressions' is the definition.
The definition and answer can be both acts as well as being plural nouns.
Perhaps they are linked in a way I don't understand?

'about illumination on hills' is the wordplay.
'about' becomes 'c' (abbreviation for circa).
'illumination' becomes 'lamp'.
'on' is a charade indicator (letters next to each other).
'hills' becomes 'downs' (I've seen this before).
'c'+'lamp'+'downs'='CLAMPDOWNS'

Can you help me to learn more?

I've seen this clue in The Daily Express.

Want a hint initially instead of a full solution? Install my app