Shake buttocks as low as possible (4,6)
I believe the answer is:
rock bottom
'low as possible' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'shake buttocks' is the wordplay.
'shake' becomes 'rock' (synonyms).
'buttocks' becomes 'bottom' (synonyms).
'rock'+'bottom'='ROCK-BOTTOM'
'as' is the link.
Can you help me to learn more?
(Other definitions for rock bottom that I've seen before include "such depths?" , "such a price is heavily reduced" , "Total despair" , "worst condition possible" , "As low as you can get" .)