Webster's Revised Unabridged Dictionary · 1913

Tantamount

Tantamount , adjective

[French tant so much (Latin tantus) + English amount.]

Equivalent in value, signification, or effect.
A usage nearly tantamount to constitutional right. — Hallam
The certainty that delay, under these circumstances, was tantamount to ruin. — De Quincey

Tantamount , intransitive verb

To be tantamount or equivalent; to amount. [Obsolete] — Jer. Taylor