Definition of "laburnum"

[…] Lord Henry Wotton could just catch the gleam of the honey-sweet and honey-coloured blossoms of a laburnum, whose tremulous branches seemed hardly able to bear the burden of a beauty so flame-like as theirs[.]

1891, Oscar Wilde, chapter I, in The Picture of Dorian Gray, London, New York, N.Y., Melbourne, Vic.: Ward Lock & Co., page 1

The trees began to come fully alive. The larches and birches were covered with green, the laburnums with gold.

1950, C. S. Lewis, chapter 11, in The Lion, the Witch and the Wardrobe, Collins, published 1998