In my vocabulary list, I have two different forms for the perfective of слышать listed: услышать and послышать. I know I'm not imagining this, because a practice deck I found online also had both verbs (although it was very unclear from the example sentences contained in that deck what the difference between the two is supposed to be).
Questions:
1. Are послышать and услышать exact synonyms, or are they not?
2. Which of the two should I memorize as the perfective form of слышать? Why?
3. Are either послышивать or послушивать actual words, and if so, are either of the two the actual imperfective form of послышать (instead of слышать)?
Attempt: I looked up the difference between the two, but the results were confusing to me.
Specifically, the English version of wiktionary doesn't list послышать as a perfective form of слышать -- it only lists услышать. послышать doesn't even have an entry in the English wiktionary, although it does have an entry in the Russian wiktionary, викисловарь.
But викисловарь lists послышать as being the perfective form of an entirely different verb: послышивать, for which it does not have an entry.
Yet this Russian dictionary seems to list послышать as being an exact synonym of услышать. I don't quite understand what meaning the example sentences are supposed to convey, however, so I could be wrong. This dictionary, despite otherwise saying the same as the previous one, also says that the imperfective form of послышать is послушивать, instead of послышивать.
This dictionary gives a very similar entry for послышать except that it doesn't mention услышать again in the item containing почуять, instead it says:
перен. Почуять, почувствовать.
According to this dictionary compiler, the difference seems to come down to whether one looks at the entry from Т.Ф. Ефремова's dictionary or the entry from Д.Н. Ушаков's dictionary.
