difference between шепнуть and прошептать?

Hi everyone - I have been trying to work out the difference between these two perfective verbs, шепнуть and прошептать and can't work it out at all!! they both seem to mean to whisper, but I am sure there will be some nuanced difference between them, can someone help please? большое спасибо - Мария

This one pretty much requires a native speaker but I could take a crack at it:

https://ru.wiktionary.org/wiki/%D1%8...83%D1%82%D1%8C
https://ru.wiktionary.org/wiki/%D0%B...B8%D1%82%D1%8C

Here's the two викисловарь pages for the words, notice the few differences, particularly in the second explanations of the meanings
Especially, that the site lists прошептать as an antonym to шепнуть (but synonyms the other way around)

Now, if you imagine the uses of "imperfectiveness" and the uses of "perfectiveness" layed out in two lists like

Imperfective
repeated
ongoing
habitual
unfinished
background-setting
process
etc.

Perfective
completed
one time, singular instance
result
etc.

So, usually it's not very important and you can just use a verb from either group (usually there only exists a pair of verbs, one of each), say, Imperfective, and in doing so technically all the meanings of that group are inherent: говорит by itself partakes of the whole list let's say; it could be ongoing, or maybe it's habitual, generally the distinction doesn't matter, just that it isn't perfective.

But! Things can get pretty complication because what if you wanted to refer to a "completed process that was repeated" versus an event that was absolutely "one-time"?

-- шептать - to whisper (imperfective)


шепнуть - perfective: single time action, short phrase, instance of communication

прошептать - perfective: lengthy process, "for a while", a whole conversation

You could imagine how these would bring to mind slightly different mental images:
шепнул - he whispered something and left
прошептал - he whispered during the whole class
шептал - he was whispering
Of course translating it like this doesn't nearly impart the internal machinery of the difference

So, some verbs break things up even further. You could have multiple perfectives (whether or not they're "the same word" is already a complicated question). In some cases, if the special perfectives also plausibly could have imperfective pairs, an infix is added. Generally speaking, the imperfective unprefixed word is the starting seed. Then, speaking metaphorically because I have no idea if this has any basis in etymological reality, a normal perfective is made as a pair to the basic imperfective, proabably with some inconspicuos prefix like 'по-', or maybe by switching -ать for -ить or -ать for -нуть. Then, say, a specified special perfective is formed, and has a particular emphasis (repeatedness over a lengthy amount of time), probably with a particular prefix meant to impart the meaning (про-, "through", as though the event is a long tunnel with duration or extent). Then finally the special perfective, made off what looks like an imperfective word (remember, it was made by simply adding a prefix to an imperfective), to get its imperfective has added into it an infix, an extra inner syllable like -ыв- .

говорить - сказать
проговаривать - проговорить

Important to remember, the ending -нуть very heavily leans towards being the kind of perfective that is single instance, one time thing, rather than being the kind of perfective that deals with completion, but I won't say that is a universal.

Here are some examples of the tree like structure of word formation I laid out:

https://en.wiktionary.org/wiki/%D0%B...B0%D1%82%D1%8C

https://en.wiktionary.org/wiki/%D0%B1%D0%B8%D1%82%D1%8C

https://en.wiktionary.org/wiki/%D1%8...B8%D1%82%D1%8C (Instead of an infix here it is a stem change)

https://en.wiktionary.org/wiki/%D0%B...B8%D1%82%D1%8C (Here the offspring-imperfectives use an ending change)

In some cases, the descendant words are equivalent to English phrasal verbs (go versus go in), in the case of the question, I guess, a more subtle reason sparked the separate words.

Спасибо болшое. That took a lot of work and it is much appreciated. Your reply makes total sense and I can now see why sometimes in the book шепнуть is used and sometimes прошептать, but couldn't see it for myself. I love learning Russian - but it can get a bit confusing can't it?
Many thanks again for this
Мария

As a native speaker I can add:
If there is no direct implications about length of the process length of 'прошептать' is very short - word or sentence. For example 'он прошептал ей на ушко всё что думал о ней' - implies very short period of time, word or clause. But anyway it's about period of time in it's core.
'шепнул' is about completed process without emphasizing that it had length.

I would say that the difference here mostly not in the length (it doesn't sound natural прошептать весь урок, though with проговорить it's quite OK). I feel the difference in the number of participants - you can шепнуть кому-либо, and that means to say sth in secret, but with the word прошептать - it's just the matter of voice level and doesn't need a specific person to refer:
"Я больше никогда его не увижу",- прошептала она, глядя на удаляющийся поезд. (she said it to herself, referring to nobody)
"Завтра жду тебя у школы", - шепнула она и убежала. (secretly, for the only one person to hear)