Act fast with fastening (9)
I believe the answer is:
tightrope
'act' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'fast with fastening' is the wordplay.
'fast' becomes 'tight' (I've seen this before).
'with' means one lot of letters go next to another.
'fastening' becomes 'rope'.
'tight'+'rope'='TIGHTROPE'
Can you help me to learn more?
(Other definitions for tightrope that I've seen before include "Cable on which acrobatics are performed" , "Acrobat's walkway" , "- - -walker" , "Acrobat's wire" , "An acrobat walks on this high above the ground" .)