Gentlemen's Agreement
noun
Remember how you learned that 紳士 means "gentleman?" Well when two men determine that the best thing to do is cooperate they form a gentlemen's agreement.
しんしきょうてい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
あいつらとは紳士協定を結んでいるはずだ。
They’re supposed to be tied to a gentlemen’s agreement.