This is the 11596th most frequent Russian word.
единственного
"The only" or "sole."
The word 'единственного' is used in its masculine singular form in the genitive case to refer to the only guest present.
Он был единственным гостем на вечеринке.
He was the only guest at the party.
Here, 'единственном' is in the masculine singular locative case, referring to the exclusive means or path discussed.
Мы говорили о единственном пути к успеху.
We talked about the only way to success.
In this sentence, 'единственному' is in the masculine singular dative case, denoting to whom her love is directed, highlighting her sole child.