Superlative form of shabby: most shabby.(adjective)
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Use "shabbiest" in a sentence
"It\'s called the shabbiest of all lies, "Silent assertion.""
"He told him that these two camps were about the worst and shabbiest he had ever seen during his year of travelling about Germany."
"I am spending time on eBay these days trying to replace the shabbiest of the ones in my collection, and also ever searching for numbers Six, Seven and Eight which I have only in bound-volume form, without their covers."