Latin gave German the -ment suffix, and the neuter gender came with it. Almost every noun ending in -ment is das. The rule covers hundreds of words. The exceptions you can count on one hand.
The rule
Every noun ending in -ment that names a thing, a process, or an abstract concept is neuter. That means das → in the Nominativ, and as the default for every case that follows. You see the ending, you know the article.
Eight words to start with:
| Word | Meaning |
|---|---|
| dasDokument | document |
| dasInstrument | instrument |
| dasExperiment | experiment |
| dasArgument | argument |
| dasParlament | parliament |
| dasFundament | foundation |
| dasMedikament | medication |
| dasElement | element |
The two exceptions
Two common words end in -ment and are masculine: derMoment (moment) and derZement (cement). Both came into German from French, where the original word had a different grammatical history that pushed it towards masculine. They didn't follow the neuter pattern.
These two are worth fixing in memory separately. Once you know them, the rule runs cleanly for everything else.
One footnote on Moment: it exists in both genders, with different meanings. der Moment is a moment in time, the one you will use every day. das Moment is a factor or an aspect: ein entscheidendes Moment, a decisive factor, and das Drehmoment, torque. Same spelling, two words.
Why it works
Most -ment words entered German from Latin via French. In classical Latin, the suffix -mentum was neuter, and German kept that gender. The result is a tightly consistent pattern across technical, scientific, and formal vocabulary → Temperament, Testament, Pigment, Sediment, Segment, Regiment, all neuter and all das.
The pattern is especially useful because many of these words look nearly identical to their English counterparts. The meaning is often transparent. Now the article is too.
See -ment, the answer is das. Memorize derMoment and derZement separately, and the rule takes care of everything else.