infinitesimal
/ˌɪnfɪnɪˈtesɪm(ə)l/adjective [原级] 无穷小的;无限小的;极小的
...mineral substances present in infinitesimal amounts in the soil. ... 土壤里含有的极微量的矿物质。
noun [抽象名词] 无限小;极微量;极小量
That great, infinitesimal question - I can't shake it out of my thoughts. 那伟大的浩瀚无涯的问题我是无法赶出脑袋了。