So, Dobrý= masculine, Dobré = neutral, but what are the feminine and the plurals?
If we are speaking about greetings etc., where the case is accusative (or 4th case) –because it is shortened "Přeji Vám dobré odpoledne" = "I wish you good afternoon"– then:
feminine: Dobrou noc = Good night
plural feminine (and masculine):
Veselé Vánoce = Merry Christmas
Veselé Velikonoce = Happy Easter
In plural neuter accusative, hard adjectives should end with á, but I dare say that standard ("correct") neuter endings are not very popular with Czechs.
I can only recommend you to have a look at declension overview (hope it won't scare you a lot): http://mluvtecesky.net/en/grammar/adjectives https://en.wikipedia.org/wiki/Czech_declension#Adjective
Does odpoledne -literally- mean something like "in the afternoon". Asking because of the "od" part :)
Literally, it means "from-noon". The opposite is "dopoledne", which means literally "until-noon". "Poledne" is "noon".
Do people say "dopoledne"?
There is an English word "forenoon" which I have never heard in real life.