We still celebrate some festivals that were important to our ancestors.

ancestors 是名词 ancestor 的复数形式。ancestor 由前缀 an-（表示"向上"）和词根 cest（来自拉丁语 cedere，意为"走"）加上后缀 -or（表示人）组成，字面意思是"往上走的人"，引申为"祖先、先辈"。