Dirty means covered in mud, dust or stains — dirty hands, dirty washing, the kitchen floor is dirty. It is the plain opposite of clean.
It has two extensions worth knowing. Dirty can mean unfair: a dirty trick, dirty tactics, playing dirty. And it can mean sexually explicit: a dirty joke, dirty magazine. Both are informal and both are common enough that a learner will meet them early. Note that dirty is also a verb — dirty your shoes — though get dirty is far more usual. The noun is dirt, and dirt cheap means extremely inexpensive.
1adjectivedirtyCovered in dirt or stains.
“Take those dirty boots off outside.”
2adjectiveunfairUnfair or dishonest.
“It was a dirty trick and he knew it.”
3adjectivesexuallySexually explicit.
“He told a dirty joke and nobody laughed.”
Too few real examples of this word to estimate which sense is commonest.
dirty is a state of being unclean.
Middle English
dirti
English, today
dirty
From Middle English dirti, alteration of earlier dritti, equivalent to dirt + y. Cognate with Middle Low German drēterich (“dirty”). See also drite.
Etymology from Wiktionary, CC BY-SA