Learn Turkish: Bu hastalık burada çok yaygın. - This disease is very widespread here.

It comes from the verb yaymak, meaning to spread or to distribute. By adding the -gIn suffix (which becomes -gın due to vowel harmony), the verb transforms into an adjective describing the state or result of that action: yaygın, meaning widespread or common.

Can I use yaygın for abstract things, or is it only for physical things spreading like a disease?

It is incredibly versatile and often used for abstract concepts. You will frequently hear it in phrases like yaygın bir inanç (a common belief) or yaygın kullanım (widespread usage). It translates well to both widespread and common in English.

As a quick refresher, how is the word hastalık formed here?

It uses the very common -lIk suffix, which creates abstract nouns from adjectives or other nouns. Here, it attaches to hasta (sick or patient) to create hastalık (sickness or disease).

Why isn't there a to be suffix at the end of the sentence, like yaygındır?

In everyday Turkish, the third-person copula suffix (-dIr) is usually left out when stating a simple, observable fact. If you said yaygındır, it would sound more like an encyclopedic statement, a formal medical report, or a general objective truth rather than a conversational observation.