Schiss haben
to be scared
(Colloquial, crude) To be very afraid of something or someone.
Ich geb's zu, ich hab total Schiss vor Spinnen.
I admit it, I'm totally scared of spiders.

fear / diarrhea
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to be scared
(Colloquial, crude) To be very afraid of something or someone.
Ich geb's zu, ich hab total Schiss vor Spinnen.
I admit it, I'm totally scared of spiders.

The word 'Schiss' is very colloquial and is considered crude or even vulgar. You should only use it in very informal situations and among friends.
Komm schon, das ist doch kein Grund, Schiss zu haben.
Come on, that's no reason to be scared.
To express fear, you use the fixed expression 'Schiss haben' (to be scared). The noun almost always appears without an article here. The fear relates to something with the preposition 'vor' + dative.
Er hat furchtbar Schiss vor dem Zahnarzt.
He's terribly scared of the dentist.
The meaning 'Durchfall' (diarrhea) is usually clear from the context (food, illness). It is often used with verbs like 'bekommen' (to get) or 'kriegen' (to get) and is also very colloquial.
Ich glaube, von dem Essen kriege ich Schiss.
I think that food is going to give me the runs.
fear
'die Angst' and 'der Schiss' can both mean that someone is very afraid. 'Angst' is the neutral word and fits everywhere. You can use it in serious, private, and official situations. 'Schiss', on the other hand, is very colloquial and crude. For example, people say 'Schiss haben' (to be scared), but more among friends or in casual language. In formal situations, 'Schiss' sounds inappropriate. Also important: in another meaning, 'Schiss' can be vulgar for diarrhea; here, however, it is about fear.

Am Telefon gab Paul zu, dass er vor der Prüfung richtig Schiss hat.
On the phone, Paul admitted that he was really scared of the exam.
Vor der Operation war die Angst in der Familie deutlich zu spüren.
Before the operation, the fear in the family was clearly noticeable.