This is the 201st most frequent German word.
einigen
To agree or to unite.
Here, 'sich einigen' emphasizes the result of a negotiation or mutual decision.
Nach langen Verhandlungen haben sie sich schließlich geeinigt.
After long negotiations, they finally reached an agreement.
'Einigen' is used as a dative pronoun meaning 'some' and refers to a specific but unspecified subset of participants.
Einigen Teilnehmern gefiel der Vorschlag.
Some participants liked the suggestion.
The reflexive verb 'sich einigen' means 'to come to an agreement' and is used here to show mutual agreement between subjects.