Not valid, acceptable, or legally binding; alternatively (pronounced /ˈɪnvəlɪd/), a person made weak or disabled by illness or injury. The context determines both pronunciation and meaning.
From Latin 'invalidus' meaning 'not strong,' from 'in-' (not) and 'validus' (strong). The legal/logical sense of 'not valid' developed in the 16th century, while the medical sense referring to disabled persons emerged in the 17th century. Both meanings share the core concept of lacking strength or effectiveness.
Invalid is a perfect example of how the same word can have completely different pronunciations and social implications - the stress shift from in-VAL-id (not valid) to IN-val-id (disabled person) reflects changing attitudes toward disability and language sensitivity. The medical usage is now often considered outdated as society moves toward more respectful terminology.
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