What is the plural possessive form of janitor?

Answer 1

A possessive shows ownership. If a janitor has a house, we'd say it was the janitor's house. Just add an apostrophe + s to any regular singular noun, then add what that noun owns (or possesses) to get the possessive form. Here are a few examples: the janitor's bucket, the janitor's son, the janitor's uniform.

Here are some others:

The teacher's smile was sweet.

I saw the robin's eggs in a nest.

When the boy's shoelaces came loose, he tripped on Joe's bookbag.

Look at the nouns that follow the possessive form. Ask yourself, "Who owns it?" The answer is~ the teacher, the robin, the boy, Joe.

Or, for your question, the janitor.

I just heard the janitor's keys in the hall.

Who owns the keys?

The janitor.

The apostrophe is added AFTER the owner and is followed by an "s" for a singular, regular noun.

Answer 2

The plural form of the noun janitor is janitors.

The plural possessive form is janitors'.

Example: The janitors' supervisor sets their schedules.

Answer 3

Janitors'