This is the 10475th most frequent Russian word.
взаимности
"Mutuality" or "reciprocity."
Here, 'взаимности' is used as a noun in the prepositional case, referring to the mutual feelings or interactions in a context of relationships.
Мы долго говорили о сути взаимности в человеческих отношениях.
We talked for a long time about the essence of mutuality in human relationships.
Here, 'взаимности' is used as a source of a positive emotion, specifically relating to her feelings being reciprocated.
Она чувствовала радость от взаимности в своих чувствах.
She felt joy from the mutuality in her feelings.
Here, 'взаимности' stands for the expected reciprocity, expressing a desire for feelings or actions to be returned in kind.