Any person with a disability or illness.
"The government agency provides special travel accommodations specifically for invalids to ensure their comfort and safety during long journeys."
In plain English: An invalid is someone who is physically weak and needs help taking care of themselves because they are sick or injured.
"The doctor told his grandfather that he was too invalid to travel alone."
force to retire, remove from active duty, as of firemen
"The mayor decided to invalidate all contracts for the remaining firefighters due to budget cuts."
To exempt from duty because of injury or ill health.
"The soldier was invalided out of the army after sustaining a severe leg wound in battle."
In plain English: To invalidate something means to make it no longer true, valid, or effective.
"The system will automatically invalidate any ticket used on a holiday."
Not valid; not true, correct, acceptable or appropriate.
"The invalid spent his days recovering in a quiet room away from the noise of the city."
Suffering from disability or illness.
In plain English: Invalid means not true, correct, or able to be accepted as valid.
"The doctor said he was still invalid from his recent surgery."
Usage: Use the adjective form to describe something that is false, incorrect, or unacceptable rather than physically broken. When referring to people, prefer terms like "person with a disability" over using this word as a noun to maintain respect and accuracy.
The word invalid comes from combining the prefix in- with Latin valid, originally meaning "not strong or effective." It entered English to describe someone who is not physically fit for duty or something that lacks legal force.