Both, or neither, depending on how you look at it. It is the past tense of the verb 'to have' and as such applies to all persons, singular and plural:
I had
You had
He/she/it had
We had
They had
Singular Plural is caterpillars
Steroids is plural. The singular form of the word is steroid.
The word crisis is singular. The plural form of crisis is crises.
its singular there is no plural form of rendezvous
Association is singular. Associations is plural.
The word team is singular; the plural form is teams.
These is plural, this is singular
Lance is singular. Lances is plural.
The word 'Phenomenon' is singular. The plural form is 'Phenomena'.
The word metastasis is singular, metastases is plural.
The word "ground" can be both singular and plural. Singular: "The ground is wet." Plural: "The grounds of the park are well-maintained."
Louse is singular. The plural form is lice.
No, the word "list" is singular. The plural form of "list" is "lists."
Verbs cannot be singular or plural. Has is after singular nouns.
It's singular. The plural is cafeterias.
Tool is singular. Tools is plural.
Caveman is singular. Cavemen is plural.