Alana is expecting her third baby -- a brother for Willow and Corran.
Alana writes: "We'd like a Scottish name, or at least a Celtic flavour but not too common. Corran is obviously rare and while Willow has now shot up the charts it wasn't in the top 100 when we picked it. Our other constraint is no C/K names - there are so many in our extended family it's become a bit of a running joke. Spelling needs to be not too difficult - my own name is either spelled wrong or pronounced wrong on an almost daily basis so I'd like to avoid that if possible.
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Looking at the names you've considered, I've noticed that all but Struan and Flynn are in the top 100 in Scotland currently. I can see your dilemma; while you don't want an especially popular name, you are drawn to names that are stylish and will be easily recognised.
That is why I haven't completely ignored the Scottish top 100, but have stuck to options below the top 50, meaning names given to fewer than 100 boys per year.
While researching options, I found myself drawn to Scottish heritage names (like Corran) with links to indigenous Scottish trees (like Willow); a perfect match between Willow and Corran and keeping the Scottish natural theme.
Aulay - From the medieval Scots Gaelic name Amladh which was itself a Scottish rendering of the Norse Olaf. It ranked at #711 in Scotland in 2020.
Blaine – From the Gaelic bla "yellow, blonde". Blane (without the i) was borne by a Scottish saint. Blaine ranks at #536 and Blane at #891 in Scotland.
Brae – A name found all over the map of Scotland, derived from the Scots Gaelic bràigh "upper part," though in some cases it may be from the Old Norse breiðr "broad." It ranks at #1274.
Euan / Ewan – A sleek Scottish heritage name with an ancient history. It likely means "born of the yew tree". The yew tree is a native Scottish tree and was sacred to the ancient Celts. Euan ranks at #126 and Ewan at #159.
Fraser – A stately Scottish clan name with a modern sound. The Fraser Fir tree is named after Scots Botanist, John Fraser. It ranks at #59.
Innes – A place name derived from the Scots Gaelic innis "island". It ranks at #83.
Lachlan – A handsome name that is quintessentially Scottish but with a Nordic heritage. It ranks at #101.
Lennox – A Scottish place name -- like Corran -- which derives from the Gaelic name Leamhnachd made up of leamhan "elm" and achadh "field". Like Willow, the elm is an indigenous tree in Scotland.
Lorcan – An Old Gaelic name derived from the Old Irish lorcc "fierce" and the diminutive suffix -án.
Magnus – This Roman name, meaning "great", became a Scandinavian royal staple in the early Middle Ages and from there passed to Scotland. Magnus was even in the top 100 in Scotland back in 1900. It currently ranks at #119.
Maxwell – A Scottish clan name, derived from a pool in the River Tweed near Kelso which means "Maccus's stream". Maccus is thought to be a Scottish form of Magnus. It ranks at #350.
Rowan – A multifaceted name that links Willow and Corran seamlessly. Firstly, Rowan is the name of a native Scottish tree which ultimately takes its name from Norse for "red" (thanks to its berries). It is also a Scottish surname derived from places named Roan (Ayr, Berwick, Roxburgh). It is also an anglicised form of the Gaelic name Ruadhán derived from the Old Irish ruad "red, red-haired"
Shay – An Anglicised form of the Scottish name Seaghdh -- the Irish form was Séaghdha -- which in Old Gaelic meant "majestic, learned, esteemed." It ranks at #164.
Sorley – A Scottish variant of Somerled and the Gaelic Somhairle which are derived from the Old Norse name Sumarliði meaning "summer-wayfarer. Somerled/Somhairle was not uncommon in medieval Scotland. Sorley ranks at #426.
Stirling – A city in central Scotland with a strong, handsome sound. It ranks at #1274.
Tavish – The Anglicised form of Thàmhais, the Scottish form of Thomas. It ranks at #891.
Tiernan – A modern form of the Old Gaelic Tighearnán meaning "little lord". It was used by royalty in medieval Ireland and Tigerna (a Latinised form) can also be found in medieval Scottish records.
Tristan – Tristan is a Celtic name that traces back to the Pictish name Drustan. It was borne by Pictish kings and one, in particular, Drustan son of Talorc, appeared in Scottish legends as saving a princess from giants when he travelled to the Hebrides. It ranks at #426.
I hope this has been of use. Best wishes with settling on the perfect name.
UPDATE: Welcome, Ruairidh!