noun
A lack of something needed
A faulty part
defect implies a lack of something essential to completeness or perfection a defect in vision; an imperfection is any faulty detail that detracts from perfection minor imperfections of style; a blemish is a superficial or surface imperfection that mars the appearance skin blemishes, a blemish on his record; a flaw is an imperfection in structure or substance, such as a crack or gap, that mars the wholeness or continuity a flaw in a metal bar
See defect in Webster's New World Roget's A-Z Thesaurus II
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