noun
'completed' stamp; 'paid' stamp
A rubber stamp used to mark documents, forms, or bills as completed, processed, or paid. Often associated with self-inking stamps like シャチハタ.
See also: シャチハタ
請求書に済印を押してください。
Please stamp the invoice with the 'paid' stamp.
この書類にはもう済印が押してある。
This document already has the 'completed' stamp on it.
A brand name often used generically for self-inking stamps, including 済印. 済印 refers to the stamp itself, while シャチハタ is the product category.
Compound of 済 (sumi, 'completed') and 印 (in, 'stamp'). The reading すみいん is a straightforward combination of the on'yomi of the kanji.