What's the collective plural of ninja?

-Like a gaggle of gease...

Thanks :D

You can use either ninja or ninjas as the plural. The majority I have seen its use is merely ninja but some places add the "s"

Nin·ja (nnj) KEY

NOUN:
pl. ninja or nin·jas
A member of a class of 14th-century Japanese mercenary agents who were trained in the martial arts and hired for covert operations such as assassination and sabotage.

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ETYMOLOGY:
Japanese : nin, to endure + ja, person (from Middle Chinese tia)

Don't believe everything you read in a dictionary.

The plural of Ninja is Shinobi.

While Japanese has no plurals, there are several mechanisms to imply singularity.

The NIN is the 'on' reading of the SHINOBI character.
The JA is derived from SHA which is the 'on' reading of the character for item/thing.
This character can sometimes act to make a word singular if no ownership statements exist.

The collective is SHINOBI-RYU or in English SHINOBI CLAN may be acceptable.