Expressions (phrases, clauses, etc.), Ichidan verb
to slip out (e.g. of a comment, remark, etc.); to utter unintentionally
to pour from one's lips (of words); to flow freely (of speech); to rush out of one's mouth
Also written 口を突いて出る【くちをついてでる】、口を衝いて出る【くちをついてでる】