1. most dirty or not clean; most contaminated with dirt, germs, or impurities
Usage: superlative form of unclean
2. most morally or spiritually impure
Usage: religious or moral context

Examples

• The basement was the uncleanest room in the entire house.
• After the flood, the kitchen became the uncleanest area we had to deal with.
• The uncleanest water samples came from the industrial district.
• In ancient texts, certain animals were considered the uncleanest creatures.
• The hospital identified the uncleanest surfaces that needed immediate attention.
• Among all the camping sites, theirs was the uncleanest one we encountered.