This is the 9864th most frequent Japanese word.
言
"言" means "word" or "speech."
言いました here is the past tense of 言う, which means 'to say'. It is used to describe the act of saying something.
彼は秘密を言いました。
He said a secret.
言葉 refers to 'word' and is a noun derived from the verb 言う, combined with the suffix 葉 that indicates articulation.
その言葉の意味を教えてください。
Please tell me the meaning of that word.
言うこと refers to 'what one says'. It turns the verb 言う into a noun phrase, indicating spoken content or opinion.