Fourthly is a pointing word for lists. You have already given three points; this next idea is number four: “Fourthly, we need to save water.” It does that one job.

Fourthly第四點 is是 a pointing word for lists一個用來列點的指示詞. You have already given three points你已經講了三點, this next idea is number four這個接下來的想法就是第四點: "Fourthly, we need to save water."「第四，我們需要省水。」 It它 does that one job就是做這一件事.

You do not use it for a race or a place in a queue — there you say fourth (“she finished fourth”).

for a race or a place in a queue在比賽名次或排隊順序上 you do not use it不會用這個字 — there那種情況下 you say fourth你會說fourth ("she finished fourth")（「她得到第四名」）.

It sounds a little stiff and old-fashioned, the kind of word you meet in a formal talk or a careful written argument. Many people now just say “fourth” or “number four” in the same slot, and that sounds more natural.

It它 sounds聽起來 a little stiff and old-fashioned有點生硬、老派, the kind of word那種字 you meet你會遇到的 in a formal talk or a careful written argument在正式演講或講究的書面論述裡. Many people now現在很多人 just say直接說 "fourth" or "number four"『fourth』或『number four』 in the same slot在同樣的地方, and that sounds more natural聽起來更自然.

Though actually, if you do use the -ly set (firstly, secondly, thirdly, fourthly), try to keep the set tidy; mixing “first” with “secondly” is common in real speech, but some careful writers dislike it.

Though actually不過其實, if you do use the -ly set如果你真的要用這一套-ly字 (firstly, secondly, thirdly, fourthly)（firstly, secondly, thirdly, fourthly）, try to keep the set tidy儘量整套一致; mixing "first" with "secondly"把『first』跟『secondly』混著用 is common in real speech在真實口語裡很常見, but不過 some careful writers dislike it有些講究的作者不喜歡這樣.