der Stöpsel
stopper / plug
An object, usually made of rubber, plastic, or cork, used to close an opening, especially the drain of a sink or bathtub.
Ich finde den Stöpsel für die Badewanne nicht.
I can't find the plug for the bathtub.

stopper / plug
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stopper / plug
An object, usually made of rubber, plastic, or cork, used to close an opening, especially the drain of a sink or bathtub.
Ich finde den Stöpsel für die Badewanne nicht.
I can't find the plug for the bathtub.

'Stöpsel' is related to the verb 'stopfen' (to stuff / to plug), which means 'to fill or close an opening.' So a 'Stöpsel' (stopper / plug) is a small thing you use to plug something.
Mit einem Korken kann man eine Flasche fest stopfen.
You can tightly plug a bottle with a cork.
You can recognize the meaning from the context: If it is about a 'Waschbecken' (sink) or a 'Badewanne' (bathtub), it refers to the stopper. If a person is being addressed affectionately, it means a small child. In the context of 'Steckdose' (socket) or 'Kabel' (cable), it means an electrical plug.
Ohne den Stöpsel läuft das Wasser aus dem Waschbecken.
Without the plug, the water runs out of the sink.
In its main meaning as a stopper for a drain, 'Stöpsel' is often used with the verbs 'ziehen' (to pull, to remove it) or '(rein)stecken' (to insert, to put it in place).
Wenn du baden willst, musst du erst den Stöpsel in den Abfluss stecken.
If you want to take a bath, you first have to put the plug in the drain.
The term 'Stöpsel' for a small child is colloquial and is usually used affectionately or in a diminutive way.
Die Oma nennt ihren Enkel liebevoll „mein kleiner Stöpsel“.
The grandma affectionately calls her grandson 'my little one.'
The use of 'Stöpsel' for an electrical plug is colloquial and common mainly in certain regions of Germany.
Kannst du mal den Stöpsel vom Fernseher aus der Steckdose ziehen?
Can you pull the TV plug out of the socket?
closure / fastener
'der Verschluss' and 'der Stöpsel' can both be used to close an opening. 'Verschluss' is the general word and can take many forms, for example a lid, button, or zipper. 'Stöpsel' is a specific object that you put into an opening, especially into the drain of a sink or bathtub. The words can be confused because a 'Stöpsel' is a type of 'Verschluss'. If you mean exactly this small part, 'Stöpsel' is more natural. If you are talking generally about closing something, 'Verschluss' fits better.

Vor dem Baden steckt Max den Stöpsel in den Abfluss.
Before taking a bath, Max puts the plug in the drain.
Der Verschluss der Flasche sitzt so fest, dass ich Hilfe brauche.
The cap on the bottle is so tight that I need help.