This is the 17340th most frequent Russian word.
тайно
Secretly.
The word "тайно" is used as an adverb, modifying the verb "встретился" to indicate the manner of the action being secretive.
Он тайно встретился с ней.
He secretly met with her.
Here, "тайно" is used as an adverb modifying "работает," emphasizing the clandestine nature of her work.
Она всегда работает тайно, не раскрывая своих планов.
She always works secretly, not revealing her plans.
In this sentence, "тайно" functions as an adverb modifying the participial form "записанный," indicating that the act of recording was carried out in secrecy.