Avrilaceous is not a word, unless you are Banvillaceous.
After some debate (see attached Google search), the general consensus is that the word has been coined by Banville to refer to Avril, whom the reader first meets on page 55. She is an incidental character who serves to illustrate the narrator's unreliable memory.
He remembers, dimly, her face 'was sprinkled all over with tiny freckles'. On page 129 the narrator refers to his own greying hair that is flecked with Avrilaceous freckles. And on page 157, when a robin appears, he remembers that Avril's freckles reminded him of something else.
Rhinophyma, according to Medline Plus, is a large bulb-shaped, red-coloured nose once thought to be caused by heavy alcohol consumption, hence the name 'grog blossoms'. However it also occurs in teetotallers. It is more common among men.
qv stands for quod vide, a Latin phrase meaning 'which see' and denoting a cross-reference.
Pierre Bonnard, a French painter maligned by Picasso as a second-rate artist, spent the last 25 years of his life painting studies of himself and of his house in Le Cannet near Cannes, France.
An exhibition of this period of work entitled The Late Interiors was held at The Metropolitan Museum of Art in 2009. It was the first show dedicated solely to Bonnard's late interiors and still lifes. Forbes has a review.
A groyne is built to defend against sea erosion of a beach and land by longshore drift. Often made of timber, groynes can also be constructed from concrete.
A woollen cloth originally handwoven on the Isle of Harris in Scotland's Outer Hebrides. In Ireland, a similar tweed is woven in Donegal.