Take the plunge (3)
I believe the answer is:
dip
This could be a double definition.
'take' is the first definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'the plunge' is the second definition.
('dip' can be a synonym of 'plunge')
Can you help me to learn more?
(Other definitions for dip that I've seen before include "Sudden sharp decrease in quantity" , "Plunge briefly in liquid" , "Thick sauce; brief swim" , "See 21" , "Immerse briefly in liquid" .)
