noun
wallet
B1
Portemonnaie means 'wallet'. It's a neuter noun (das Portemonnaie) with plural Portemonnaies; as a loanword it forms an -s plural (unusual for German). Declension follows foreign-s plural; genitive/des/dem forms show -s. No reflexive or auxiliary issues; common synonyms: Brieftasche. It is colloquially common.
Examples
Die Verkäuferin fand ein Portemonnaie, weil ein Kunde es auf dem Tisch liegen ließ, und sie übergab es der Polizei.
The saleswoman found a wallet because a customer had left it on the table, and she handed it over to the police.
Ich habe mein Portemonnaie zu Hause vergessen.
I forgot my wallet at home.
Ich habe mein Portemonnaie zu Hause vergessen.
I forgot my wallet at home.
Details
Mnemonics
Picture a small leather wallet that holds cards and cash.
Portemonnaie sounds like French 'porte-monnaie' — 'port(e)' (carry) + 'money' = wallet.
Portemonnaie is 'das' — think 'das Portemonnaie' (the wallet), a small object.