Dear Svetlana,

Here the meaning of the word 'leaf'  is not literal. It is metaphorically used.

See http://www.thefreedictionary.com/metaphorical

Best wishes,

Subir.

Dear Svetlana, no, they are not alwais used in their first meaning. Meaning arises when connecting the word to the underlying semantic space, which is, on the other hand, activated by the context, by the personal experience, goals and intents. In this sense, each time a word is used, it is to give a "novel" meaning - this created  within the discourse." To turnover a new leaf" could refere to the first meaning if it was a part of conversation in a lab of biological studies.

I would say that the most common use of the word "leaf" is leaves on a tree. However with respect to books, "leaf" is usually used as a verb, i.e. to leaf through a book. Leaf can also mean "hinged flap on the side of a table" is from 1550s" because pages in a book are also hinged.  

So you are correct that "leaf" meaning a page of a book is a secondary meaning and a is metaphor. Metaphors do not always use the most common meanng

Hi Svetlana, you might want to take a look at Construction Grammar as a body of thought.  There is an English language handbook: The Oxford Handbook of Construction Grammar  Edited by Thomas Hoffmann and Graeme Trousdale and an unrelated website (link included) that might be useful places to start.  The principles look broadly generalizable, but I am only familiar with bits of the English language work on the topic.  Essentially, some things we learn and use as words, some as phrases - which may or may not be combinatorially construable - and some as routines.

http://www.constructiongrammar.org/