What does `只` mean in `他有四本书，可是我只有三本`? In the following sentence:

他有四本书，可是我只有三本。


, what does the 只 mean?

I think the sentence reads He has four books, but I have three.

I also read the sentence like 我只需要一个叉子, though I cannot get what 只 works for in the sentence.

Note that when I looked up 只 in my dictionary, it says the following:

classifier for birds and certain animals, one of a pair, some utensils, vessels etc


So I don't get what it means. What does it function for?
In Simplified Chinese, 只 is polyphonic. In the sentence, 只 means only, pronounced zhǐ. The meaning you cited corresponds to another pronunciation, zhī, of the character.