discussion a detailed conversation about sth that is considered to be important 指重要事情的讨论、谈论、商讨：◆Discussions are still taking place between the two leaders. 两位领导人仍在进行讨论。
conversation a talk, usually a private or informal one, involving two people or a small group; the activity of talking in this way 通常指私下的或非正式的交谈、谈话：◆a telephone conversation 电话交谈
dialogue conversations in a book, play or film 指书、戏剧或电影中的对话、对白：◆The novel has long descriptions and not much dialogue. 这部小说描述多，对话少。A dialogue is also a formal discussion between two groups, especially when they are trying to solve a problem or end a dispute. * dialogue 亦指两个团体间为解决问题或结束争端进行的正式对话、讨论、交换意见：◆The President told waiting reporters there had been a constructive dialogue. 总统告诉等候的记者，刚才进行了一次富有建设性的对话。
talk a conversation or discussion, often one about a problem or sth important for the people involved 常指对有关人员就某个问题或重要的事情进行的交谈、谈话、讨论、商讨：◆I had a long talk with my boss about my career prospects. 我和老板就我的事业前景进行了一次长谈。
debate a formal discussion of an issue at a public meeting or in a parliament. In a debate two or more speakers express opposing views and then there is often a vote on the issue. 指公共集会上或议会里就某问题进行的、常以表决结束的辩论：◆a debate on prison reform 关于监狱制度改革的辩论
consultation a formal discussion between groups of people before a decision is made about sth 指团体间在决策前进行的咨询、商讨、磋商：◆There have been extensive consultations between the two countries. 两国之间进行了广泛磋商。
chat a friendly informal conversation; informal talking 指友好的非正式交谈、聊天 NOTE The countable use of chat is especially British English. * chat 作可数名词尤用于英式英语：◆I just called in for a chat about the kids. 我只是打电话来随便聊聊孩子的事情。
gossip a conversation about other people and their private lives 指关于他人及其私生活的闲谈、闲聊、说长道短：◆We had a good gossip about the boss. 我们讲了好一会儿老板的闲话。

Patterns

a discussion/conversation/dialogue/talk/debate/consultation/chat/gossip about sth
a discussion/conversation/dialogue/debate/consultation on sth
in (close) discussion/conversation/dialogue/debate/consultation with sb
to have a discussion/conversation/dialogue/talk/debate/consultation/chat/gossip with sb
to hold a discussion/conversation/debate/consultation

[C]

(

disapproving

)

a person who enjoys talking about other people's private lives 喜欢传播流言蜚语的人；爱说长道短（或说三道四）的人speakercommunicator ◇ gossip ◇ talker

These are all words for a person who talks or who is talking, especially in a particular way. 以上各词均指说话者，尤指以某种方式说话的人。

speaker a person who is or was speaking; a person who speaks a particular language 指发言者、讲某种语言的人：◆I looked around to see who the speaker was. 我四下环顾看说话的是谁。◆a fluent Arabic speaker 阿拉伯语讲得流利的人
communicator (rather formal) a person who is able to describe their ideas and feelings clearly to others 指交际者、交流者：◆The ideal candidate will be an effective communicator. 理想的候选人定要是善于沟通的人。
gossip (disapproving) a person who enjoys talking about other people's private lives 指喜欢传播流言蜚语的人、爱说长道短（或说三道四）的人：◆Myra is a dear, but she's also a terrible gossip. 迈拉是很可爱，但也是个讨厌的长舌妇。
talker a person who talks in a particular way or who talks a lot 指以某种方式说话的人、爱说话的人：◆He's a very persuasive talker. 他是一个说话很有说服力的人。◆She's a (great) talker(= she talks a lot). 她很健谈。

speaker or talker? 用 speaker 还是 talker？

Talker is used when you are talking about how much sb talks or how well they talk. It is not used for the person who is or was talking. * talker 用以指说话多或少，或者话说得如何的人，不用以指正在或曾经在说话的人：◆I looked round to see who the talker was. You can say that sb is a good/persuasive speaker but that means that they are good at making speeches. If you mean that they speak well in conversation, use talker. * good/persuasive speaker 指的是擅长演讲的人。如果指健谈或能言善辩的人就用 talker。