From The Collaborative International Dictionary of English v.0.48 [gcide]:
Praying \Pray"ing\,
a. & n. from Pray, v.
[1913 Webster]
Praying insect, Praying locust, or Praying mantis
(Zool.), a mantis, especially Mantis religiosa. See
Mantis.
Praying machine, or Praying wheel, a wheel on which
prayers are pasted by Buddhist priests, who then put the
wheel in rapid revolution. Each turn in supposed to have
the efficacy of an oral repetition of all the prayers on
the wheel. Sometimes it is moved by a stream.
[1913 Webster]