My employment contract stated that I entitle 13 month salary.
So I think employer cannot say that the  13th month payment is a bonus.
Bonus means the employer can pay me 10 times of my monthly salary and can also
pay me nothing.

However, my employer said that due to hk economy is not good he has to delay
paying me the 13th month salary until further notice.

He is so meant and so cunning. "further notice" does not mean he won't pay me.

Can I suit him for not paying my salary on time ?

I also want to know. Is it illegal for company doing that?

<<My employment contract stated that I entitle 13 month salary>>
I also want to know the entitled 13 month salary means 12m basic salary plus extra bonus or guranteed 13m basic salary?

Many thanks