tantamount
Concise Oxford English Dictionary © 2008 Oxford University Press:
tantamount/ˈtantəmaʊnt/
▶adjective (tantamount to) equivalent in seriousness to; virtually the same as.
– origin C17: from the earlier verb tantamount ‘amount to as much’, from Ital. tanto montare.
'tantamount' also found in these Oxford entries:

