main

Compared meaning: important or most significant (adjective).

比较义项：重要的、主要的（形容词）。

• main 本词

  Neutral, common word for the chief or most significant one among several; used before nouns like reason, cause, road, or point; suitable in both everyday and formal contexts.

  中性常用词，指几者中最主要或最重要的一个；常用在reason、cause、road、point等名词前；日常和正式场合都可使用。

  The main reason for the delay was bad weather.

  延误的主要原因是恶劣天气。

• primary

  Formal or technical, emphasizing first in importance or rank, often in official, academic, or medical contexts (primary goal, primary source, primary concern); sounds more objective than main.

  较为正式或专业，强调在重要性或次序上排在第一位，常用于官方、学术或医学语境（primary goal主要目标、primary source第一手资料、primary concern首要关切）；听起来比main更客观。

  Improving safety is the primary goal of this new policy.

  提高安全性是这项新政策的首要目标。

• great

  Suggests importance combined with admiration or high esteem, often describing achievements or contributions, in a formal or slightly literary tone; great also means 'excellent', a different sense not compared here.

  表示重要之余还带有敬重或高度评价的意味，常用于描述成就或贡献，语气较正式或带文学色彩；great也可表示“极好的”，此处不作比较。

  He made a great contribution to modern physics.

  他为现代物理学做出了伟大的贡献。

• big

  Informal and conversational, emphasizing how much something matters or affects someone, common in casual speech (big deal, big decision); big also simply means large in size, a different sense not compared here.

  口语化、随意，强调某事对某人有多大影响或多重要，常见于日常口语（big deal重大的事、big decision重大决定）；big也可单纯表示体积大，此处不作比较。

  Losing that client was a big deal for our small business.

  失去那个客户对我们这家小公司来说是件大事。

Main, primary, great, and big all mean important. Main is neutral; primary is more formal. Great adds admiration; 'excellent' is not compared. Big is informal; 'large in size' is not compared. Primary's senses 'first, as in an election' and 'a color' are not compared.

这几个词在“重要”这一义项上意思相近，但语气和正式程度不同：main和primary比较中性客观，primary更正式，常用于官方或专业场合；great带有敬重、赞赏的意味，语气较正式或文学化；big则比较口语化，常用于日常表达重要性。这里不比较great的“极好的、令人愉快的”义项，也不比较big的“体积大”义项，以及primary的“首要的／初级的（如primary election初选、primary color原色）”等其他义项。