According to Donald Parry, parallelism is universally recognized as the characteristic feature of biblical Hebrew poetry. (p. i)
Apparently, the prophets and writers of the scriptures employed the repetition of alternating parallel lines for the purpose of reinforcing their teachings and doctrines. (p. x)
When a group of three or more words, similar in sense but not identical in meaning, come together in a verse or passage with characteristics which parallel one another, this is called Synonymia, or "synonymous words." (p. xlix)
A good example of Synonymia occurs in Ether 8:16 which talks about the secret oaths: "And they were kept up by the power of the devil . . . to help such as sought power
to gain power
and to murder
and to plunder
and to lie
and to commit all manner of wickedness
and whoredoms.
[Donald W. Parry, The Book of Mormon Text Reformatted according to Parallelistic Patterns, F.A.R.M.S., p. 465]