pewno is a form of "pewny" and that is from
zach. psł. *pъvьnъ 'taki, który spełni oczekiwania, godny zaufania' (the one that will fulfil expectations, trustworthy)
"pewno" does not exist in Polish anymore outside of this expression, but it used to be neuter form of that adjective.
I would say literal translation is "for certain"
literal: "for certain", "for sure"; ironic: "leave it out"
"Na pewno" is an idiomatic expression, coming from Old Polish neuter gender adjective "pewno" [sure, certain; secure; reliable; unwavering], which was created from Old Slavic noun "pъva" [certainty, reliability; confidence] See: "na pewno"
Similar expressions: "na nowo" - [anew, afresh, from the beginning]; "na okrągło" - [around the clock; all the time], "na prawo" - [to the right].
I would disagree based on where the emphasis falls. "This book is certainly boring" sounds like you are reading the book and confirming that it is indeed boring.
"Certainly this book is boring" sounds more like you would be asking someone who is reading it why they are doing so, since the book is most certainly a boring one. It puts the stress of "certainly" on the specific book compared to other books, rather than on the book being boring as compared to not boring (as is in the first case.) I can't really imagine this sounding natural in any way outside of a question form.
However, I am not sure how or even if the polish translation would differ between these two pretry similar meanings.
What makes you think that it should be correct?
"Nudna" is an adjective in female form, because "książka" is a female gender noun.
An adjective always follows the gender and number of the noun it describes. The Polish verb "być" (to be) requires nouns to be in Instrumental Case, and if there is an adjective associated with the noun, it has to follow:
- This book is certainly a boring book = Ta książka na pewno jest nudną (adj. Instr. fem. sing.) książką (noun Instr. fem. sing.)
- This book is certainly a masterpiece = Ta książka na pewno jest arcydziełem (noun Instr. neutr. sing.)
But this rule does not apply to adjectives separated from the noun! If the noun is left behind or omitted at all - the isolated adjective is in Nominative case:
- This book is certainly boring= Ta książka na pewno jest nudna (adj. Nom. neutr. sing.)
"Nudnej" is "nudna" in Genitive case. Genitive Case may occur in negation sentences regarding the verb.
- I do not have a boring book - Nie mam nudnej (adj. Gen. fem. sing.) książki (non Gen. fem. sing.)
But if the negation does not refer to a verb, but to adjective, it is in Nominative Case;
- This book is not boring - Ta książka nie jest nudna (adj. Nom. neutr. sing.)
And if the negation is about the noun, it is similar as in indicative:
- This boring stuff is not a book - To nudne coś nie jest książką (noun Instr. fem. sing.)
I can see that Polish the same as English has evolved over a couple of generations, the English was once a beautiful language, with the advent of computer and cellphone it has eroded. We don't teach cursive in our schools anymore, next all communication will be phonetic because it's too complicated for the current generation. Pzeprasham pana, nashe ludzie sa legate.
I can agree and disagree, Ben. As an everyday language, I don't really consider it beautiful, although this may depend very much on the speaker. But it's especially the lack of rules which gives English its flexibility and makes it a great playing field for poetry. And I'm not only talking about old times, I also find a lot of beauty in today's English songwriting.