Talking about the weather is a non-controversial topic for small talk when meeting someone for the first time.

non-controversial 是由前缀 non-（表示"非、不"）和形容词 controversial（有争议的）组成的复合形容词。controversial 来自名词 controversy（争议），加上形容词后缀 -ial 构成。non-controversial 字面意思是"没有争议的"，指不会引发分歧或争论的话题。