Verb for to talk

I've been told

話す means to speak
言う means to say
語る means to tell
談 means to talk

The last one is where i'm confused because from what i've learnt so far だん cannot be a verb, so what does 談 actually mean and is there another verb used to express speech i haven't mentioned ?

喋る　shaberu: talk, chatter

談 is a noun meaning "conversation". It seems to be rarely used by itself, but mostly in compounds such as 冗談（じょうだん）, which means "joke".

談 is also used in 相談: discussion, consultation

Like 安倍氏談(Abe-shi dan; Mr.Abe talked), 談(dan) is sometimes used at the end of the report about interview.
I think it's short for 談ず(danzu; discuss) or 談じた(danjita; talked) and the typical abbreviated style of the newspapers or magazines.

しゃべる sounds more casual than 話す ;
語る sometimes sounds more formal than 話す .

Among 言う , しゃべる , 話す , 語る and compounds beginning or ending with 談 ,
only しゃべる and 話す can directly take a noun meaning a language,
and usually only 語る can directly take a noun meaning a topic or a theme.
e.g.
日本語をしゃべる and 日本語を話す mean to speak Japanese language,
but we do NOT say 日本語を言う or 日本語を語る to express this sense.
e.g.
When we say 日本語を語る , here 日本語 is a topic or a theme or so,
and this phrase means to talk / tell about Japanese language.

話す and 語る can indirectly take a noun meaning a topic or a theme.
e.g.
事故 [jiko] に ついて 話す means to talk / tell about an accident.
科学技術 [kagaku-gijutsu] に ついて 語る means to talk / tell about science technologies.

I suppose 言う does not imply people's talking.
e.g.
When a chairperson asks in a meeting
" この議題 [gidai] について、ほかに言うことはありますか？ ",
he/she is asking whether any person among the members has something else to say about the topic for the meeting.

言う sometimes means to refer to, especially in written Japanese.
e.g.
A とは B を言う means A refers to B.

P. S. :
You might encounter another かたる , which means to disguise oneself as.
e.g.
郵便局員をかたる男 means a man disguising himself as a post-office clerk.

Thankyou very much for the responses. I have a much better understanding now.