All 4 Uses

solemn
in
A Christmas Carol, by Charles Dickens
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It was a great surprise to Scrooge, while listening to the moaning of the wind, and thinking what a solemn thing it was to move on through the lonely darkness over an unknown abyss, whose depths were secrets as profound as Death: it was a great surprise to Scrooge, while thus engaged, to hear a hearty laugh.†
p. 80.6

solemn = very serious--possibly dignified
As the last stroke ceased to vibrate, he remembered the prediction of old Jacob Marley, and lifting up his eyes, beheld a solemn Phantom, draped and hooded, coming, like a mist along the ground, towards him.†
p. 91.8
He felt that it was tall and stately when it came beside him, and that its mysterious presence filled him with a solemn dread.†
p. 93.6 *
The Phantom was exactly as it had been, but he dreaded that he saw new meaning in its solemn shape.†
p. 114.2

Definitions:

(1) (solemn)
in a very serious (and often dignified) manner
(2) (meaning too rare to warrant focus)
Less commonly, solemn can mean that something was done with great or appropriate ceremony. It can also be used to describe something as dark or undecorated.