Of the smallest amount (7)
(Other definitions for minimal that I've seen before include "Very small, the least possible (7)" , "Of a smallest amount" , "Very little" , "Of the least possible size" , "barely worth considering" .)
(Other definitions for least that I've seen before include "No more petty" , "Smallest (in significance)" , "Steal (anag)" , "Of minimal significance" , "Opposite of most" .)