also: にゃにゃ
interjection
Onomatopoeic representation of a cat's meow; used as an interjection or in imitation.
猫が「にゃんにゃん」と鳴いた。
The cat meowed, 'meow meow'.
noun
Childish or affectionate word for a cat; used mainly by or to small children.
あそこににゃんにゃんがいるよ。
Look, there's a kitty over there.
noun, noun or participle which takes 'suru'
sexual intercourse; making out
Slang euphemism for sexual activity; often used in a playful or indirect manner.
彼らはにゃんにゃんしてるらしいよ。
I heard they're getting it on.