Difference Between Ill and Sick

Both the words Ill and Sick have the same meaning. When a person is not feeling well or is in an undesirable health condition, such a person is known to be sick or Ill.

Both words are often used interchangeably, but both of them have distinct meanings. Initially, ill and sick tend to be associated with each other, providing the similar message to the reader. Someone who is not well. They are similar in concept but have evident variations in their use.

Ill vs Sick

The main difference between Ill and Sick is that Ill is used to refer to disease and ailments, which last for short/longer duration of time and it is used in more of a formal manner. In contrast, on the other hand, the word Sick is used to refer to disease and ailments, which last for a short period of time and is used commonly in an informal manner.

Ill vs Sick

Comparison Table Between Ill and Sick

Parameter of ComparisonIllSick
Refers toThe term ‘ill’ refers to serious diseases such as a stroke.The term ‘sick’ refers to something, not such severe as feeling nauseous.
LanguageThe word ‘ill’ is used as a formal term. The word ‘sick’ is more of an informal term.
Duration of Disease and AilmentsLong term durationShort term duration
TypeIt includes more severe and major conditions.It includes more minor conditions.
Largely used for referring toHumans tend to fall ‘ill’.Only animals only tend to be sick. for example, a sick cow and other non – human things such as a sick joke, a sick land, sick economy, etc.
OriginThe word ‘ill’ has originated from the Old Norse term ‘illr’.The word ‘sick’ has originated from the English term ‘soec’.

What is Ill?

An individual is said to be ill if he is feeling unwell, either mentally or physically. Ill is a word which sounds more formal than sick and is also used in written form of English. This is why we prefer to use the term ill instead of sick for writing an application.

While in British English, word Ill is significantly used to refer to a person’s physical medical condition. Ailments and diseases which require medical attention regardless of their duration fulfil the criteria of being referred to an illness. An individual who is suffering from a medical condition is a person who is ill irrespective of if he/she has heart problems or just the flu.

What is Sick?

An individual suffering from a disease is known as a sick person. When a person feels the urge to vomit such person is known to be sick. A sick mind is a term that is used to describe a person who is psychologically or emotionally troubled. Sometimes when a person says that he’s sick of parties, he means to say that he’s bored and annoyed while attending parties, and he doesn’t want to visit any more parties. One might even be sick of another person.

Sick and tired is yet another idiom that describes a person who is tired and fed up with something or a situation.

In general, however, sick is a term that is used when a person has some sort of disease, illness, or vomiting. It is usual for those suffering from nausea to be considered sick.

Main Differences Between Ill and Sick

  1. The word Ill is usually related to a disease or something serious whereas the word Sick, on the other hand, is often used to refer to mild ailments such as cold, cough, fever, sore throat, etc.
  2. The word Ill is used formally, whereas the word Sick is used informally.
  3. Ill refers to disease and ailments, which last for longer duration whereas Sick refers to disease and ailments of which last for a short period of time.
  4. Americans more casually use the word Sick whereas the word Ill is formally used by English people.
  5. Observe the use of word Sick with several nouns such as a sick dog, a sick leave or homesick. On the other hand, the use of word Il with nouns such as ill leave or ill sick will sound absurd and meaningless.
  6. Use of term Ill in words such as mentally ill or ill repute sounds appropriate due to their formal manner and adverse effects related to it. On the other hand, If one will say mentally sick or sick repute, then such words may not hold the same formal touch or meaning to them.
  7. When an individual is said to be sick of someone, he/she wants to say that they are annoyed or irritated of that person. On the other hand, saying a person is ill of someone does not make any sense.


Ill and Sick are two most common words used worldwide as people fall sick or ill from time to time. The concept of both words are somewhat similar and can be used interchangeably.

Concept of word Ill involves suffering from a disease, an illness or feeling unwell. Sick, on the other hand typically include when a person is physically sick or is sick of an individual, may also be used to denote an object or a system that is not functioning correctly, namely a sick economy.

Sick can also denote that an individual is tired of a particular thing. Sick is slighter formal among these two terms. It typically includes disease or ailments of a short period of time, namely flu, and a majority of the time it is used to indicate the state of nausea.

Whereas, Ill is a more formal term used to denote illness or disease of longer durations. An individual who is not in a healthy state as a result of a medical condition such as cancer or heart disease can be referred to as ill. On the other hand, an individual running a mild fever or state of cold can also be considered ill. Just like sick, ill also take into account the feeling of nausea.

A clear distinction between the terms is that when someone is not feeling well due to some kind of serious medical issues, that person is said to be Ill. On the other hand, when a person is not feeling well due to some minor issue such as cold or flu then such person is said to be Sick.


  1. https://search.proquest.com/openview/75702d95c0ce2ea847f746c195b39959/1?pq-origsite=gscholar&cbl=37022
  2. http://grad.litu.tu.ac.th/assets/public/kcfinder/upload_grad_web/public/MA-ELT_The8th%20LITU%20Graduate%20Conference%202019.pdf#page=43
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