stamp
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stamp
A device, usually made of wood or plastic with a rubber surface, used to print ink onto a surface in order to add a mark, date, or symbol.
Der Beamte nahm den Stempel und drückte ihn kräftig auf das Dokument.
The official took the stamp and pressed it firmly onto the document.
Careful: 'der Stempel' (stamp) is not a postage stamp. A postage stamp is called 'die Briefmarke' in German. 'Der Stempel' is the device used for stamping (rubber stamp) or the imprint made with it.
Ich brauche noch eine Briefmarke für diesen Brief nach Italien.
I still need a postage stamp for this letter to Italy.
Whether the device (meaning 1) or the imprint (meaning 2) is meant is often revealed by the verb. If you 'use' a Stempel or 'take it in your hand', it is the device. If a Stempel 'is' on a document, 'is missing', or you 'get' one, it is the imprint.
Bitte nehmen Sie den Stempel und markieren Sie die Akte.
Please take the stamp and mark the file.
In the figurative meaning, 'Stempel' (label/stigma) is often used in fixed expressions. Common ones are 'jemandem einen Stempel aufdrücken' (to put a label on someone) or 'einen Stempel bekommen' (to be given a label).
Man hat ihr den Stempel einer Lügnerin aufgedrückt.
They labeled her a liar.
seal
'Siegel' and 'Stempel' both have to do with an imprint or a mark. A 'Stempel' is often the device used to stamp something onto paper, or the stamp mark itself. A 'Siegel' is a special, usually official imprint or sign that confirms authenticity, security, or quality. The words can be confusing because a 'Siegel' can be made with a 'Stempel'. But not every 'Stempel' is a 'Siegel': a date stamp in an office is just a mark, while a 'Siegel' has a confirming or protective function.
Am Empfang bekommt jedes Formular einen Stempel mit dem heutigen Datum.
At reception, every form gets a stamp with today's date.
Das Siegel auf dem Vertrag zeigt, dass das Dokument offiziell ist.
The seal on the contract shows that the document is official.