查了幾個有關公告的詞，以下是自己的釋義
一般用 announcement
官方性質 proclamation, declaration
更正式、組織或政府對外用 declaration
較簡易 bulletin
可口頭或文字形式 announcement, declaration
一群人或政黨對外用 menifesto
proclamation
1. an official statement about something important that is made to the public;
the act of making an official statement 宣言；公告；聲明
noun countable uncountable
2. A proclamation is a public announcement about something important,
often about something of national importance.
announcemet
1. a spoken or written statement that informs people about something
（一項）公告，佈告，通告 countable
- Today's announcement of a peace agreement came after weeks of discussion.
經過幾週的討論之後，今天公佈了和平協議。
- Announcements of births, marriages and deaths appear in some newspapers.
有些報紙刊登出生、結婚、死亡通告。
2. the act of publicly informing people about something （指行動）宣佈，宣告
uncountable
- Announcement of the verdict was accompanied by shouts and cheers.
在一片喊叫和歡呼聲中宣佈了正式判決。
declaration
1. an official or formal statement, especially about the plans of a government or an organization;
the act of making such a statement 公告；宣告；宣言 countable uncountable
- to issue/sign a declaration 發佈／簽署公告
- the declaration of war 宣戰
- the Declaration of Independence(= of the United States)
（美國）獨立宣言
2. a written or spoken statement, especially about what people feel or believe
聲明（書）；宣佈；表白；宣稱 countable
- a declaration of love/faith/guilt 表白愛情；表達信念；宣判有罪
3. an official written statement giving information 申報（單） countable
- a declaration of income 收益申報表
- customs declarations
(= giving details of goods that have been brought into a country)
報關單（帶入境內物品的詳細清單）
bulletin
1. a short news report on the radio or television （電台或電視台的）新聞簡報
2. an official statement about something important 公告；佈告
- a medical bulletin on the President's health 關於總統健康狀況的醫療報告
3. a printed report that gives news about an organization or a group
（機構或組織的）簡報
manifesto
1. a written statement in which a group of people, especially a political party,
explain their beliefs and say what they will do if they win an election
宣言 noun
-
an election manifesto 競選宣言
-
the party manifesto 政黨宣言
資料來源：Google 字典
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