Impure means mixed with something that should not be there. Impure water, impure metal, impure thoughts.
In chemistry and metallurgy it is a plain technical description: an impure sample contains other substances, and how impure is measured. In religious and moral use it means unclean or sinful, and impure thoughts is a phrase from confession and catechism. Note impurity, which as a plural means the contaminants themselves; and purify, which does the opposite work.
1adjectiveimpureMixed with something that should not be there.
“The gold was impure, mixed with copper and silver.”
2adjectivemorallyMorally unclean.
“The priest warned the boys against impure thoughts.”
impure is a quality of contamination.
Latin impurus is in- plus purus, clean. Pure, purge and Puritan come from the same cleanness.
Latin
impūrus
Middle French
impur
English, today
impure
From Middle French impur, from Latin impūrus.
Etymology from Wiktionary, CC BY-SA
Practised in Word Building