onceadv.一次；曾经conj.一旦n.一次adj.曾经的once application一次性施用once up on a time从前oncethroughboiler直流锅炉Once is enough.一次就够了。once over lightly从头到尾马马虎虎地once run kerosene直馏煤油Once Through Load直流负荷Once is no custom一次不成例once-fired ware一次烧成的制品once in a while b时而; 有时