die Spritze
syringe
A medical instrument with a needle and a barrel, used to inject fluids into the body or remove them from it.
Die Ärztin bereitete die Spritze für die Impfung vor.
The doctor prepared the syringe for the vaccination.

syringe / shot
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syringe
A medical instrument with a needle and a barrel, used to inject fluids into the body or remove them from it.
Die Ärztin bereitete die Spritze für die Impfung vor.
The doctor prepared the syringe for the vaccination.

The noun 'die Spritze' (syringe/shot/sprayer) is derived from the verb 'spritzen' (to spray/squirt). This verb means to expel a liquid quickly and under pressure, which connects the different meanings of the noun.
Der Gärtner spritzte die Pflanzen mit Wasser.
The gardener sprayed the plants with water.
To describe an injection, fixed verb combinations are used. The doctor 'gibt eine Spritze' (gives a shot), while the patient 'bekommt eine Spritze' (gets a shot) or 'kriegt eine Spritze' (gets a shot, informal).
Ich muss morgen zum Arzt gehen, um eine Spritze zu bekommen.
I have to go to the doctor tomorrow to get a shot.
The verb often reveals whether the instrument or the injection is meant. Verbs like 'vorbereiten' (to prepare) or 'aufziehen' (to draw up) refer to the instrument, while 'bekommen' (to get) or 'geben' (to give) usually refer to the injection as an action.
Die Arzthelferin zog die Spritze mit dem Impfstoff auf.
The medical assistant drew up the vaccine into the syringe.
You can recognize the non-medical meaning from the context. Words like 'Wasser' (water), 'Garten' (garden), 'Kinder' (children), or 'Feuerwehr' (fire department) indicate that a device for spraying liquids is meant.
Bei der Hitze war die Wasserschlacht mit den Spritzen eine tolle Abkühlung.
In the heat, the water fight with the squirters was a great way to cool off.
shot
'Schuss' and 'Spritze' can both have to do with an injection. 'Spritze' is the normal word for the medical instrument or for the injection itself. For example, at the doctor's you say that you are getting 'eine Spritze' (a shot / injection). 'Schuss' in this meaning is colloquial and is especially used in connection with drugs. That is why, in everyday medical contexts, you should almost always say 'Spritze'. The words can be confusing because both refer to a liquid that enters the body, but the tone and context are very different.

Vor der Reise bekommt Lisa beim Arzt eine Spritze.
Before the trip, Lisa gets a shot at the doctor's.
In dem Film braucht der Abhängige wieder einen Schuss.
In the film, the addict needs another shot.