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
The possessive adjective 'their' is a plural pronoun, used to describe a noun as belonging to two or more people or things.
Examples:
Mike and Mark went fishing with their father.
The books were half price because their coverswere missing.
They went to school carrying their lunches.
The singular possessive adjectives are: his, her, its.
No, the word had is a verb or an auxiliary verb; the past tense of to have (has, having, had).
Verbs cannot be singular or plural. Has is after singular nouns.
Their refers to more than one persons belongings. It would be plural.
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.
Association is singular. Associations is plural.
its singular there is no plural form of rendezvous
The word team is singular; the plural form is teams.
These is plural, this is singular
if a word refers to a single item it is singular. if it refers to lots of things it is plural."Potato" is singular "potatoes" is a plural word."mouse" is singular, "mice" is a plural word."person" is singular, "people" is a plural word.
The word 'she' is in singular form. The plural for 'she' would be 'they'.
"Have" may be singular or plural: I have; we have.
The word metastasis is singular, metastases is plural.
No, the word "list" is singular. The plural form of "list" is "lists."
Caveman is singular. Cavemen is plural.
Verbs cannot be singular or plural. Has is after singular nouns.
It's singular. The plural is cafeterias.
Tool is singular. Tools is plural.
Singular Plural is caterpillars