the holy grail
noun[S]
uk/ˌhəʊ.li ˈɡreɪl/us/ˌhoʊ.li ˈɡreɪl/(alsothe Holy Grail)
acupbelievedto have been used byJesusChristat themealbefore hisdeath
圣杯（传说耶稣在最后的晚餐上使用过）
something that isextremelydifficulttofindor get
极难找到（或得到）之物
Sustainednuclearfusionis theholygrail of thepowerindustry.能持久反应的核聚变是电力工业梦寐以求的“圣杯”。