[weiming]

Also, just to be nice and complete, let's review all the functions of "only" that weve come across.

First, look at the word, we can see the root "on. (one)" in the adverb. It is similar to "solely" meaning "the only one" and this is probably the earliest meaning.

Only (1)the only one
"Only we can save you, no one else."
"He is the only one who can operate it."
"This car is the only one of its kind."
"When you get there, speak to him only."
"You don't have to pay, you only have to register."

(2)something that the speaker feels is too small, or
smaller or less than expected.
"He should have given me four, I only got three."
"When he came back from the war, he only had one arm."
"Most people lost two arms, he only lost one."
"I wanted him to compensate me for the accident, he only apologised."

(2a)something that is smaller by comparison to
the same number/amount.
"There used to be many parks here, now there are only a few."
"We started with ten suggestions, but now we only have nine left."

(3)informally, to express that an action is simple or easy
"You have only but to call, and I will come." (You just have to call.)
(NOT "You only have to call." which means you don't have to do anything else (1))
"If you only tried harder, you would be a much better athelete." (You just have to try harder.)
(NOT "You only have to try harder" which means, you don't have to do anything else (1))

This use of only is often imaginary, a situation which has not happened but which could.

So, did I miss any?