就 &才 就 (imply) 早 快 容易 顺利 才 (imply) 晚 慢 不容易 不顺利 8：00点上课 他7：00就来了 早(which implies i think he came too early) 8：00点上课他7：00才来 晚 (late) 我看了一遍就记住了 快(fast) 我看了十遍才记住 慢(slow) 我去了一次就买到了. 容易 顺利(easy) 他去了三次才买到 . 不容易 不顺利(not easy)

I am wondering whether you know the character 木 which means tree and also looks like a tree （has three branches and three roots）. OK,才 looks like 木，however lack one stoke. The original meaning of 才 is 木之初（the beginning growing phrase of a tree），so you can understand now it's meaning “just” and “only”. (tree just grows; tree only grows a little) ：P

"才" does means "more than expected". Let's say: "we traveled 2 days and expected to spend 500yuan, but actually we spent 200yuan." We saved 300yuan, that is more than our expection of spending 500yuan. In this situation, we'd better use "才" to express this emotion. Can you get it now?

In fact,we must be based on the concrete context to make certain it's meaning. A Chinese word maybe have a lot of meaning. The same word is used in differrent sentences can express the meaning and tone . In above sentences,“才"is adverb.It has two usages when "才"is adverb,one of it is amounting to "just"(just now),the other is expressing low quantity or low degree. The second usage has two underlying sense in terms of its applications.One of it have the underlying sense of "more than expected".So the 才 is equel to "only".The second sentence's "才"has this sense. The other sentence have underlying sense of "just".I can describe it well,here is a example sentence,"He is just a child".The sense of "just" is equel to the"才" of the first sentence.

才花了一百块 = only 100, but I expected more. That is the correct definition of 才. The one you give above is not correct. Cheers.