They were thought of as slightly eccentric.

thought 是动词 think 的过去分词形式，think 的意思是"认为、思考"。 of 是介词，表示"关于"或"属于"的关系。 as 是介词，表示"作为"或"以...身份"。 thought of as 是一个固定短语，意思是"被视为"或"被认为是"，用来表达人们对某人或某事的看法。