The doctor gave him some tranquillizers before the surgery to calm his nerves.

tranquillizers 是名词 tranquillizer 的复数形式。tranquillizer 由词根 tranquill（平静、安宁）加上名词后缀 -izer（表示"使...的东西"）构成，字面意思是"使人平静的东西"，即"镇静剂"。