Most of the interest in the song’s meaning has concentrated on the modern version, based on Padraic Colum’s poem, so I’ll start there.
The original poem starts with the narrator looking forward to the wedding day and enjoying the sight of his “young love” at the fair. The lady in question assures the narrator that neither her brothers nor her parents will have any objection to the match, and reminds him that the day itself isn’t far away. He watches her moving away through the fair – the market – and this seems to please him.
But verse three jars; what of “the sorrow that never was said”? Is it a secret? Whose secret? Is it dissatisfaction? Is it something else? It has been suggested that the “sorrow” is an illness: tuberculosis, which was common at the time. And why was that the last that he saw of her? Does she die? Does she run off with another? Do her family change their minds? Does she just disappear, mysteriously?
I think that the mystery is key to the popularity of this song – along with the hauntingly beautiful melody, of course.
Later versions make a significant alteration to the interpretation by changing just one word. In verse 4, Colum’s “young love” (who appears in a dream) becomes a ghostly “dead love” who visits the narrator. Here we have the answer to the question raised at the end of verse 3 ( it is a shame that so many singers omit this verse). It is now evident that she dies. Now her assurance that the two of them will soon be wed is ominous: will the narrator die, too?
Ghost story or otherwise, there are still a few archaic expressions that may need explaining.
lack of kind – I think that the most likely meaning for this is “lack of kin”, ie the narrator has no family to support him (perhaps he is an orphan, a foundling or his family are so unspeakable that he has forsworn them).
An alternative possibility is the lack of “goods and commodities as distinguished from money” (definition from Merriam-Webster), as used in the phrase “payment in kind”. While many are convinced by this explanation, I am not; why the distinction between belongings and cash? You could, of course, argue poetic licence, which could be enough.
It has also been suggested that this could be “lack of kine”, where kine is cattle, and so the narrator is either poor or not a farmer; however, Colum wrote “kind”.
In the alternate lyric version of the song, the narrator is in want of years, ie he is deemed too young.
the fair – the market. It has been suggested that it is a meadow with flowers, but the alternate version talks specifically about “hand clappen dealers”, which implies buying and selling. The pertinent Oxford definition is a periodic gathering for the sale of goods.
one star awake – early evening. Just one star is showing in the sky (probably the evening star, which is actually the planet Venus).
the swan in the evening – quite literally, a swan in the evening. There is no point looking for deeper meaning here; the swan is employed as a poetical device to describe her graceful movements.
no two were e’er wed – no two people were ever married.
a sorrow that never was said – this is ambiguous. I read it as an unfortunate open secret (perhaps she has had a child out of wedlock; perhaps it is his dreadful family that I alluded to above). Others have read it as referring to a disease – TB (tuberculosis ) was mentioned by one poster (Chris) in this Mudcat thread. It may also refer to the fact that there is always sorrow in this life.
her goods and her gear – a long and poetical way of saying “the things she is carrying”. Things she has bought or is selling; equipment or tools.
no din – no noise, quietly.