Small measure of spirits (3)
(Other definitions for tot that I've seen before include "Rum measure" , "Aggregate for infant" , "Small measure for a small child" , "nipper" , "A wee dram" .)
(Other definitions for nip that I've seen before include "severe cold" , "Small drink or small bite" , "Light bite" , "Pinch or squeeze sharply" , "Quick, sharp, bite" .)