aggregate, total, totality
amount, total
center, Centre, CORE, essence, gist, heart, heart and soul, inwardness, kernel, marrow, meat, nitty-gritty, nub, pith, substance
sum total, summation
join, Union
amount, amount of money, sum of money
ADD, add together, add up, sum up, summate, tally, tot, tot up, total, tote up
sum up, summarise, summarize