The name Peninnah in the Bible
Peninnah is one of two wives of a Levite from Ramathaim-zophim in Ephraim, whose name is Elkanah, son of Jeroham (1 Samuel 1:2). Elkanah's other wife is named Hannah and she is remembered as becoming the mother of Samuel the judge.
Peninnah and Hannah's situation is somewhat similar to that of Leah and Rachel, in that Peninnah has children but is unloved, while Hannah is deeply desponded for not having children even though she's loved. The son she finally gives birth to will judge Israel for about fifty years, and will also author (it is assumed) at least parts of the books of Samuel. He never mentions the names of his half-siblings, the children of Peninnah.
Etymology of the name Peninnah
The name Peninnah comes from the root verb פנה (panah), or its by-form פנן (pnn):
The name Peninnah seems to closest resemble the latter noun, meaning coral or pearls.
For a meaning of the name Peninnah, Jones' Dictionary of Old Testament Proper Names reads Coral. NOBSE Study Bible Name List reads Coral, Pearl.