precariousyoudaoicibaDictYouDict[precarious 词源字典]
precarious: [17] Precarious comes from Latin precārius (source also of English prayer), which meant ‘obtained by asking or praying’. It was originally used in English as a legal term, in which ‘obtained by asking’ had undergone a slight change in focus to ‘held through the favour of another’. This introduced the notion that the favour might be withdrawn, and that the possession was therefore uncertain, and so the adjective soon came to be used for ‘depending on chance or caprice’ and, in the 18th century, ‘risky’.

Latin precārius was derived from prex ‘prayer’, a close relative of precārī ‘ask, entreat, pray’, from which English gets pray.
=> pray[precarious etymology, precarious origin, 英语词源]
precarious (adj.)youdaoicibaDictYouDict
1640s, a legal word, "held through the favor of another," from Latin precarius "obtained by asking or praying," from prex (genitive precis) "entreaty, prayer" (see pray). Notion of "dependent on the will of another" led to extended sense "risky, dangerous, uncertain" (1680s). "No word is more unskillfully used than this with its derivatives. It is used for uncertain in all its senses; but it only means uncertain, as dependent on others ..." [Johnson]. Related: Precariously; precariousness.