What's the difference between onomast and onomatopoetic?

Onomast

Definition:

Example Sentences:

(1) These proofs came from various demographic and onomastic characteristics of ethnic groups as well as from genetic chronology of ethnic history which is in good concordance with actual historical chronology of ethnic groups.
(2) Based on historical evidence, the origin of the ancestors, and the onomastic analysis of the families surnames, we propose that the mutation of 11 beta-hydroxylase deficiency in Jews from Morocco may have originated in either the ancient Jewish settlers or the native Berber tribes who lived in the region of the Atlas Mountains in the southern region of Morocco before the destruction of the Second Temple by the Romans, in the year 70 C.E.

Definition:

(a.) Of or pertaining to onomatopoeia; characterized by onomatopoeia; imitative; as, an onomatopoetic writer or word.

Example Sentences:

(1) Verbal originality scores were obtained from Onomatopoeia and Images, Form 1B, given t0 182 deaf Ss aged 10 to 19 yr. Ss who had been taught the onomatopoetic words scored higher than Ss who had not been taught the words.
(2) Besides phonation and articulation there are morphological, psychomotoric, onomatopoetic, and isotopic disorders.