只 and 只是 "just"
The adverb 只
只 
is used to delimit the scope of something. It comes before a predicate expressed by a verb.
is used to delimit the scope of something. It comes before a predicate expressed by a verb.Scheme
只
verb
Examples
我只买了一本书，没有别的
I only bought one book, nothing else
wǒ zhǐ mǎi le yì běn shū, méiyǒu biéde
我只学习，不工作
I only study. I don’t work
wǒ zhǐ xuéxí, bù gōngzuò
只 is used to form another adverb — 只好 . It expresses an unwanted action that has to be done because there is no other choice.
只好 comes before the verb.
. It expresses an unwanted action that has to be done because there is no other choice.
只好 comes before the verb.Examples
这次我们没有办法，只好同意
This time we have no choice but to agree
zhè cì wǒmen méi yǒu bànfǎ, zhǐhǎo tóngyì
雪下得很厉害，我们只好留在家里
It's snowing heavily outside, we'll have to stay at home
xuě xià de hěn lìhai, wǒmen zhǐhǎo liú zài jiālǐ
The adverb 只是
只是 can be used instead of 只.
can be used instead of 只.
Examples
我只是对历史感兴趣
I'm only interested in history
wǒ zhǐshì duì lìshǐ gǎnxìngqù
我只是开玩笑，你别在意
I'm just kidding, don’t worry
wǒ zhǐshì kāiwánxiào, nǐ bié zàiyì
Sometimes 只 and 只是 convey slightly different shades of meaning.
Let’s compare:
我只吻了她
我只是吻了她
我只是吻了她
只是 can also serve as a conjunction "however", "but then".
Examples
我想跟他一起去电影院，只是心里对他还有些生气
I want to go to the cinema with him, but I'm still a little angry with him
wǒ xiǎng gēn tā yìqǐ qù diànyǐngyuàn, zhǐshì xīnlǐ duì tā hái yǒuxiē shēngqì