Least possible (7)
(Other definitions for minimum that I've seen before include "Nadir" , "Least possible quantity" , "Lowest value" , "Lowest point" , "Least recorded value" .)
'least possible' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for minimal that I've seen before include "Token" , "Very little" , "barely worth considering" , "Least possible; negligible" , "Of the least possible size" .)