basic

Compared meaning: basic or foundational (adjective).

比较义项：基本的，基础的（形容词）。

• primary

  Primary stresses that something is the chief or foremost one among several, not its simplicity; it typically modifies goal, aim, source, or concern, e.g. primary goal, primary source.

  primary 强调某事物在若干项中是首要的、最重要的，而非强调简单程度；常修饰 goal（目标）、aim（意图）、source（来源）或 concern（关切），如 primary goal（首要目标）、primary source（主要来源）。

  Reading is the primary goal of this class.

  阅读是这门课程的首要目标。

• elementary

  Elementary describes the simplest, introductory level of a subject, often contrasted with advanced work; it typically modifies school, level, particle, or explanation, e.g. elementary school, elementary mistake.

  elementary 描述某学科最简单、入门阶段的水平，常与“进阶的”相对；常修饰 school（学校）、level（水平）、particle（粒子）或 explanation（解释），如 elementary school（小学）、elementary mistake（低级错误）。

  My daughter just started third grade at the elementary school.

  我女儿刚在小学开始读三年级。

• basic 本词

  Basic marks something as an essential, indispensable component that everything else builds on; it commonly modifies skills, needs, grammar, or facts, e.g. basic needs, basic training.

  basic 表示某事物是不可或缺、构成一切基础的组成部分；常修饰 skills（技能）、needs（需求）、grammar（语法）或 facts（事实），如 basic needs（基本需求）、basic training（基础训练）。

  Learning basic grammar helps you write clearer sentences.

  学习基础语法有助于你写出更清晰的句子。

• underlying

  Underlying points to a hidden, unstated cause or structure beneath the visible surface; it typically modifies cause, reason, problem, or assumption, e.g. underlying cause, underlying tension.

  underlying 指隐藏在表面之下、未明说的原因或结构；常修饰 cause（原因）、reason（理由）、problem（问题）或 assumption（假设），如 underlying cause（根本原因）、underlying tension（潜在的紧张关系）。

  The doctor searched for the underlying cause of his headaches.

  医生在寻找他头痛的根本原因。

Primary, elementary, basic, and underlying can all mean basic, but the focus differs. Primary means first or most important. Elementary means simple, an early stage. Basic means an essential part. Underlying means a hidden, unstated cause. Earliest and physics-particle senses are not compared.

这几个词都可译为“基本的”，但侧重点不同：primary 强调“首要、最重要”；elementary 强调“入门、简单的基础阶段”；basic 强调“不可或缺的构成部分”；underlying 强调“表面之下、未明说的根本原因”，四者的常见搭配也不同，不能随意互换。这里不比较 primary 表示“最早的、最初的”（如 primary election 预选）以及 elementary 在物理学中表示“基本粒子”的用法（elementary particle）。