It tightens a nut in a cleaning machine (6)
I believe the answer is:
washer
This could be a double definition.
'it tightens a nut in a cleaning' is the first definition.
The definition suggests a singular noun which matches the answer.
'machine' is the second definition.
(I have seen 'Laundry machine ' mean 'washer' so perhaps 'machine' could also mean 'washer')
Can you help me to learn more?
(Other definitions for washer that I've seen before include "keep things firm" , "Ring under a nut" , "Flattened ring that keeps nuts secure" , "Cleaner" , "Tap seal" .)