Shannon

It's not 'Abha na tSionnainn'. It's 'Abha na Sionnainne'.

I don't think that etymology is right. River Shannon is Abha an tSionna in Irish. Those familiar with Irish will notice that (very) roughly means "river of Sionna", Sionna {SHO-nuh} being a water goddess once worshiped in the region associated with wisdom (as most water goddesses are).

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It's clear with the first syllable: "sean" and "sion" in Irish are pronounced distinctly, though the difference is mostly lost to English speakers. Also, while abhainn does indeed mean river, it is shortened to abha in most dialects; it is unlikely the most commonly dropped part would be retained in a name. Lastly, adjectives and nouns work the other way around in Gaelic languages (river-old, not old-river), making the given etymology even more improbable. [noted -ed]

Shannon can be used as a nickname for Shenandoah, a use for which I have actually seen before.

The name Shannon can also mean, along with "small, wise one", "small/young warrior", which is practically the same as the meaning of the name Evan, which is "young warrior". Just thought I should let you guys know.

This name is NOT from the Shannon River in Ireland; it is Teutonic for 'armored warrior-maid'. This meaning makes it definitively feminine.

In a baby book I saw somewhere, it said the meaning was "little wise owl." I like this name.

Shannon is actually Irish and it is after the River Shannon in Ireland.

* (may be folk-etymology)
Shannon (Eng) > S'Anann (Gadelic) > Sidhe Anann "Faery of the River Goddess, River-Sprite." var. S'Ana < Shawna (Eng), Si'Ana < Shiana (Eng), possibly also S'Aine < Shania (Eng).

Also, as a male name fairly common in Ireland, > 'Seanan', diminutive of 'Sean' "the wise." Attested.

Shannon means "Godly wisdom" and "Little Warrior".

Shannon also means "Wisdom".