-mentum

Derived from the Latin suffix -menta in collective nouns like armenta (“herd, flock”). Latin -menta is from Latin -mentum (singular), from Proto-Italic *-məntom, from the plural Proto-Indo-European *-mn̥teh₂ (*-mn̥ + *-teh₂, plural of *-mn̥-to-).^[1]

• (Classical Latin) IPA^(key): [ˈmɛn.tũː]
• (modern Italianate Ecclesiastical) IPA^(key): [ˈmɛn̪.t̪um]

-mentum (plural -menta)

1. instrument, medium, or result of; e.g. monumentum

Second-declension noun (neuter).

• http://etimologias.dechile.net/latin/?Sufijos
• Dictionnaire Étymologique de la Langue Grecque by Pierre Chantraine. Paris, 1968.