This is the 7748th most frequent Japanese word.
口実
"Excuse" or "pretext."
In this sentence, 口実 is used to mean 'pretext,' indicating an excuse made up to hide true intentions.
彼の話は偽りの口実だったことが明らかになった。
It became clear that his story was a false pretext.
Here, the word 口実 means 'pretext' to create an opportunity for an action or conversation.
新しい企画の話をする口実に、彼を夕食に誘った。
As a pretext to discuss the new project, I invited him to dinner.
Here, 口実 is used to mean 'excuse,' specifically one given to justify an action or decision.