equivalent vs tantamount

equivalent is a noun but tantamount is not a noun.

Word	Noun	Adjective	Verb	Adverb
equivalent	Yes	Yes	No	No
tantamount	No	Yes	No	No

As adjectives, equivalent and tantamount are synonyms defined as:

equivalent (noun)	tantamount (noun)
the atomic weight of an element that has the same combining capacity as a given weight of another element; the standard is 8 for oxygen
a person or thing equal to another in value or measure or force or effect or significance etc

equivalent (adjective)	tantamount (adjective)
being essentially equal to something	being essentially equal to something