tan ‧ ta ‧ mount /ˈtæntəmaʊnt/ BrE AmE adjective
[ Date: 1600-1700 ; Origin: tantamount 'something equal in value' (1600-1700) , from Anglo-French tant amunter 'to amount to as much' ]
be tantamount to something if an action, suggestion, plan etc is tantamount to something bad, it has the same effect or is almost as bad:
To leave a dog home alone is tantamount to cruelty.