noun, noun which may take the genitive case particle 'no'
one's only trick; the one thing one knows; a one-track mind
Often used critically to describe someone who keeps repeating the same idea, phrase, or method because it is all they know. Common in the phrase 一つ覚えのように.
He repeats the same story like a broken record.
That politician's speeches are all about tax cuts—it's his one and only message.