Arabic has words that mean many while being shaped like one. They are not broken plurals, and they do not carry the sound-plural endings. There are two kinds, and they are easy to confuse.
| Singular? | ||
|---|---|---|
| Ism al-jam' | قَوْم · رَهْط · جَيْش | none from the same root |
| Ism al-jins al-jam'i | شَجَر · تَمْر · نَحْل | add a ة — شَجَرَة, تَمْرَة, نَحْلَة |
Both are singular in shape, and that is what decides the agreement you will see around them.
اِسْم الجَمْع has no singular from its own root. قَوْم means a people; there is no قَوْمَة. اِسْم الجِنْس الجَمْعِيّ does have one, and you make it by adding a ة: شَجَر is trees, شَجَرَة is a tree; تَمْر is dates, تَمْرَة is one date.
Why it matters when you read. Both are singular in form, so agreement usually follows the singular — and the Quran uses that freedom deliberately, sometimes agreeing with the form and sometimes with the meaning.
Do not read these as broken plurals. A broken plural is a plural — رِجَال is the plural of رَجُل. A collective noun is a singular word for a group, which is why it can take singular agreement.
The test is the ة. If adding one gives you the single item — شَجَر → شَجَرَة — it is اِسْم الجِنْس الجَمْعِيّ. If nothing gives you a singular of that root — قَوْم — it is اِسْم الجَمْع.
Is a collective noun the same as a broken plural?
No. A broken plural is the plural of a singular that exists in the same form. A collective is a singular word for a group — either it has no singular of its own shape at all, or its singular is made by adding a ta' to it.
Next in the guideصِيغَة مُنْتَهَى الْجُمُوعWhat is the ultimate-plural pattern (sighat muntaha al-jumu')? →Updated