noun which may take the genitive case particle 'no'
tens of millions; countless thousands
Used as a no-adjective to express an extremely large, indefinite number, often in literary or emphatic contexts.
Countless thousands of stars shone in the night sky.
Tens of millions of people saw that movie.
Compound of 幾 (iku, 'how many') + 千万 (senman, 'ten million'). The combination creates a literary expression for an immense, indefinite number.