Tantamount (adjective)

Equivalent in seriousness or importance; virtually the same.

Origin:

Late 16th century: from tantamount, on the pattern of words such as paramount.

Examples:

1. His failure to attend the meeting was tantamount to insubordination.
2. This mistake is tantamount to a disaster.
3. His behavior was tantamount to treason.
4. Leaving the door open is tantamount to an invitation to thieves.
5. The results of the experiment were tantamount to a breakthrough in the field.