About the word 'つつがなく' (Tsutsu naku)

The word 'つつがなく' (tsutsu naku), often used in business, letters, and formal settings. This 'つつが' (tsutsu ga) is written as '恙' and, according to ancient language, means illness, disaster, or worries. '恙無く' (tsutsu naku)... means to be spending time peacefully and without incident. Therefore, '恙無くお過ごしください' (tsutsu naku osugoshi kudasai) means 'Please take care of yourself and spend your time peacefully and without incident.' For '恙' (tsutsu), if you type 'つつがなく' (tsutsu naku), it will appear in predictive text, so please try it. It's a kanji that isn't commonly used... or rather, it's a kanji that's almost exclusively used in '恙無く' (tsutsu naku) nowadays. And it makes sense, as this word was used in a national letter sent to Prince Shotoku over a thousand years ago. Words from over 1000 years ago are still in use today. Amazing, isn't it?