windig
windy
Characterized by strong or noticeable wind.
Heute ist es draußen ziemlich windig, du solltest eine Jacke anziehen.
It's pretty windy outside today; you should put on a jacket.

windy / shady
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windy
Characterized by strong or noticeable wind.
Heute ist es draußen ziemlich windig, du solltest eine Jacke anziehen.
It's pretty windy outside today; you should put on a jacket.

The adjective 'windig' (windy/shady) is derived from the noun 'der Wind' (the wind) with the ending '-ig'. This pattern is very common for forming adjectives from nouns (e.g., Sonne → sonnig).
Auf dem Berggipfel war es sehr windig.
It was very windy on the mountain peak.
You can recognize the meaning from context. If people are talking about the weather, a place, or nature, the literal meaning is intended. If 'windig' (windy/shady) refers to a person, a business, or an explanation, the figurative, negative meaning ('unseriös' — dubious/untrustworthy) is intended.
An der Küste ist es oft windig.
It is often windy on the coast.
In the literal meaning, 'windig' (windy) is often used in the impersonal construction 'es ist windig' (it is windy) to describe the weather.
Nimm einen Schal mit, es soll heute windig werden.
Take a scarf with you; it's supposed to get windy today.
In the colloquial meaning 'unseriös' (dubious/untrustworthy), 'windig' (shady) is often combined with nouns like 'Typ' (guy), 'Geschäft' (business/deal), 'Firma' (company), or 'Ausrede' (excuse).
Er hat mir eine windige Ausrede erzählt, warum er das Geld nicht zurückzahlen kann.
He gave me a shady excuse for why he can't pay the money back.
reputable / respectable
'seriös' and 'windig' form a clear contrast in this meaning. 'seriös' describes a person, company, or offer as trustworthy and proper. 'windig' means colloquially that something seems questionable or untrustworthy. The word can also describe the weather, but in this contrast it is not about wind; it is about trust. If a business seems honest and credible, it is 'seriös'. If it looks like a trick, an excuse, or a risk, you can call it 'windig'.

Das windige Geschäft im Internet hat viele Kunden misstrauisch gemacht.
The shady online business made many customers suspicious.
Die Bank hat mir ein seriöses Angebot für den Kredit gemacht.
The bank made me a reputable offer for the loan.