To break a promise, especially about money you owe or a deal you agreed to — you take the benefit and then do not pay up. It goes with 'on': welsh on a bet, welsh on a debt, welsh on a promise, welsh on an agreement.

To break a promise指違背承諾, especially about money you owe or a deal you agreed to尤其是關於你欠的錢或你同意的交易 — you take the benefit and then do not pay up你拿了好處卻不付帳. It goes with 'on'這個字要搭配'on': welsh on a bet, welsh on a debt, welsh on a promise, welsh on an agreement像welsh on a bet（賴掉賭注）、welsh on a debt（賴帳）、welsh on a promise（食言）、welsh on an agreement（毀約）

It came out of British racecourse slang for a bookmaker who took people's bets and then disappeared, and it still carries that flavour: not merely failing to pay, but slipping away from an obligation you clearly accepted.

It came out of British racecourse slang它源自英國賽馬場的俚語 for a bookmaker who took people's bets and then disappeared指收了大家賭注就跑路的組頭, and it still carries that flavour而且到現在還帶著那種味道: not merely failing to pay不只是沒付錢, but slipping away from an obligation you clearly accepted而是從一個你明明已經接受的義務裡偷偷溜走

It is informal, and it is an accusation — you use it when you are angry, and the person accused will feel insulted.

It is informal這是非正式用語, and it is an accusation而且帶指控意味 — you use it when you are angry你會在生氣的時候用它, and the person accused will feel insulted被指控的人會覺得受到侮辱

Here is the part that matters most for you: many people, Welsh people above all, hear this as an insult to Wales and its people, and consider the word offensive. Dictionaries now mark it that way. Whether the origin really is the national name is disputed, but that does not change how it lands.

Here is the part that matters most for you對你來說最重要的部分在這裡: many people, Welsh people above all很多人，尤其是威爾斯人, hear this as an insult to Wales and its people會把這個字聽成是對威爾斯和威爾斯人的侮辱, and consider the word offensive認為這個字帶冒犯性. Dictionaries now mark it that way現在字典也是這樣標註的. Whether the origin really is the national name is disputed這個字的來源是否真的和國名有關還有爭議, but that does not change how it lands但那並不改變它聽起來的感覺

Understand it when you read it; in your own English, say 'go back on', 'back out of', or 'not pay up' instead. You will lose nothing and offend nobody.

Understand it when you read it看到這個字時聽懂就好; in your own English換成你自己要講的英文, say 'go back on', 'back out of', or 'not pay up' instead改說'go back on'、'back out of'，或'not pay up'. You will lose nothing and offend nobody這樣你不會損失什麼，也不會冒犯到任何人

(Note the spelling 'welch' is also seen, and the separate ordinary meaning of Welsh — 'of Wales' — is written with a capital W.)

(Note the spelling 'welch' is also seen注意拼法'welch'也看得到, and the separate ordinary meaning of Welsh另外Welsh還有一個不相關的普通意思 — 'of Wales'——「威爾斯的」 — is written with a capital W這個要用大寫W.)