hard

Compared meaning: firm and hard to press or break (adjective).

比较义项：坚固、坚硬（形容词）。

• solid

  Solid describes something firm and dense all the way through, not hollow or shaky, emphasizing sturdy overall structure rather than surface texture.

  solid 形容物体从里到外都坚实、不空心、不摇晃，强调整体结构牢固，而不是表面质地。

  The old wooden staircase felt solid, so we didn't worry about it collapsing.

  这座旧木楼梯感觉很坚固，所以我们不担心它会塌。

• hard 本词

  Hard describes a surface that resists pressure, scratching or cutting, focusing on texture rather than the object's overall sturdiness.

  hard 形容表面能抵抗压力、不易被划伤或切开，侧重的是质地本身，而不是物体整体是否牢固。

  The diamond is so hard that it can scratch almost any other material.

  钻石非常坚硬，几乎能划伤其他所有材料。

Both describe something firm and strong, but focus differently. Solid describes something dense and sturdy all the way through, not hollow. Hard describes a surface that resists pressure or scratching. Hard's other meaning, difficult, as in a hard problem, is not compared here.

这两个词都可以形容物体质地坚实、不易变形，但侧重不同：solid 强调物体内部密实、结构牢固、不空心；hard 强调表面坚硬、不易被按压或划伤。这里不比较 hard 的另一个常见义项“困难的”（如 a hard problem）。

Compared meaning: difficult to do or deal with (adjective).

比较义项：困难的，不容易做到或应付的（形容词）。

• challenging

  Emphasizes that a task tests or stretches someone's abilities in a stimulating way; often used approvingly, suggesting effort leads to growth rather than mere hardship.

  强调某件事以激励性的方式考验或锻炼一个人的能力，常用于褒义，暗示努力会带来成长，而不只是艰辛。

  She took a challenging new role that pushed her to learn skills she'd never used before.

  她接受了一份有挑战性的新工作，促使她学习了以前从未用过的技能。

• tough

  Suggests a difficulty that demands endurance, toughness, or emotional strength; more informal and often implies hardship or strain rather than an opportunity for growth.

  暗示这种困难需要毅力、坚韧或情感上的力量来应对；语气更口语化，常暗含艰辛或压力，而不是成长的机会。

  Losing his job right before the holidays was really tough on the whole family.

  在假期前失业对整个家庭来说真的很艰难。

• hard 本词

  The plainest, most common word for difficult; neutral and informal, used in everyday speech and fixed expressions without any special connotation.

  是表示“困难”最普通、最常用的词；语气中性、口语化，常用于日常表达和固定搭配中，没有特殊的感情色彩。

  I find it hard to say no to free food.

  我发现很难拒绝免费的食物。

• difficult

  More formal and neutral than hard; common in written or professional contexts, describing a task or situation as requiring much effort, without emotional coloring.

  比 hard 更正式、更中性，常用于书面语或正式场合，描述某件事需要付出很多努力，不带感情色彩。

  The committee found it difficult to reach a unanimous decision on the budget.

  委员会发现很难就预算问题达成一致意见。

All four mean difficult, but differ in tone. Challenging is positive: a task that tests and builds skill. Tough is informal, stressing hardship and endurance. Hard is the plainest, neutral word. Difficult is more formal than hard. Tough's sense of physically strong is not compared.

这四个词都可以形容“困难的”事情，但语气和用法不同：challenging 带褒义，强调考验并锻炼能力；tough 更口语化，强调需要毅力去承受艰辛；hard 是最普通、最中性的日常用词；difficult 比 hard 更正式，多用于书面或正式场合。这里不比较 tough 表示“坚韧的、不易折断”的物理意义。

Compared meaning: needing a lot of effort (adjective).

比较义项：费力的（形容词）。

• hard 本词

  The plain, all-purpose word for effort, physical or mental; neutral in tone and far more common in everyday speech than the other three.

  “费力的”最普通、最通用的说法，可指体力或脑力上的努力；语气中性，在日常口语中比另外三个词常见得多。

  This math problem is harder than I expected.

  这道数学题比我预想的要难。

• arduous

  A formal word for a task, journey or process that demands great and often prolonged effort, usually in writing rather than casual speech.

  一个正式用词，指需要巨大且往往是长时间努力的任务、旅程或过程，多用于书面语而非日常口语。

  After an arduous three-day trek, the hikers finally reached base camp.

  经过三天费力的跋涉后，徒步者们终于到达了大本营。

• strenuous

  Focuses on physical exertion or energy used, and is the standard word in fitness or medical contexts, such as advice to avoid strenuous exercise.

  强调所耗费的体力或精力，是健身或医学语境中的标准用词，例如建议避免剧烈运动时常用此词。

  Doctors advised her to avoid strenuous exercise until her knee healed.

  医生建议她在膝盖痊愈之前避免剧烈运动。

• punishing

  Stresses the exhausting, harsh toll an activity takes on the body, often describing an extreme schedule, pace or climb rather than a single task.

  强调某项活动给身体带来的令人精疲力竭、严酷的消耗，常用来形容极端的日程、节奏或攀登，而不是单一的任务。

  The team endured a punishing schedule of five games in six days.

  这支队伍忍受了六天内打五场比赛的高强度消耗赛程。

All four mean needing much effort. Hard is plain and common. Arduous is formal, for long, demanding tasks or journeys. Strenuous means physical effort, common in fitness contexts. Punishing means an exhausting toll on the body, like a harsh schedule. Other senses are not compared.

这几个词在“费力的”这一义项上意思相近，但正式程度和适用范围不同：hard最口语化、最通用，脑力体力皆可用；arduous多用于书面语，形容长时间或艰巨的任务和旅程；strenuous强调体力消耗，常见于运动或医学语境；punishing则强调活动对身体造成的极度疲惫感，常形容高强度的日程或节奏。这里不比较hard的其他常见义项（如“坚硬的”“严厉的”），也不比较punishing表示“惩罚性的”（如punishing tax）的义项。