The noun etiology can be countable or uncountable. In more general, commonly used, contexts, the plural form will also be etiology. However, in more specific contexts, the plural form can also be etiologies e.g. in reference to various types of etiologies or a collection of etiologies.

Is etiology plural or singular?

noun. eti·​ol·​o·​gy | \ ˌē-tē-ˈä-lə-jē \ plural etiologies.

Is etiology and aetiology same?

Aetiology is the preferred spelling in some countries, including the UK, whereas "etiology" without an "a" has taken over in the US. The word "aetiology" comes from the Greek "aitia", cause + "logos", discourse.