Declan

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The Japanese word

一旦

is pronounced
ittan | いったん
means
once, for a moment, one morning, temporarily
Examples:
列車は一旦停車した。
ressha wa ittan teisha shi ta.
The train stopped for a moment.
一旦風呂&飯落ち、40分ぐらいして帰還!
ittan furo ando meshi ochi, yon zero fun gurai shi te kikan!
Break for bath & food, back in about 40 minutes!
いつもお世話になっていますから、一旦緩急あれば、すぐさま馳せ参じます。
itsumo osewa ni natte i masu kara, ittan kankyū are ba, sugusama hase sanji masu.
You're always there for me, so if you're ever in dire straits, just let me know and I'll come running.
数字を足したり引いたりという面倒臭い仕事も一旦始めてしまえば、それはそれで面白さがあるものだよ。
sūji o tashi tari hī tari toyū mendōkusai shigoto mo ittan hajime te shimae ba, sore wa sorede omoshiro sa ga aru mono da yo.
Once you go ahead and start, even the tiresome work of adding and subtracting figures is interesting in its way.
Examples sourced from tatoeba.org