Wine drinking, like square root? (7)
I believe the answer is:
cassava
'root?' is the definition.
(I have seen 'Starchy root ' mean 'cassava' so perhaps 'root' could also mean 'cassava')
'wine drinking like square' is the wordplay.
'wine' becomes 'cava' (type of Spanish wine).
'drinking' means one lot of letters goes inside another.
'like' becomes 'as'.
'square' becomes 's' (abbreviation).
'as'+'s'='ass'
'cava' going around 'ass' is 'CASSAVA'.
(Other definitions for cassava that I've seen before include "starchy food" , "tree" , "Manioc, source of tapioca" , "Staple food, the source of tapioca" , "Tropical food" .)