All 9 Uses

ruinous
in
The Silver Chair
(Auto-generated)

Jill had just time to see that it was a tower — a partly ruinous tower, with a lot of ivy on it, she thought — when she found herself ducking to avoid the archway of a window, as the Owl squeezed with her through the ivied cobwebby opening, out of the fresh, grey night into a dark place inside the top of the tower.†
Chpt 4
I have often heard the name of the giantish City Ruinous, but never met any who would tell me the way thither.†
Chpt 6
And in Harfang you may or may not hear tidings of the City Ruinous, but certainly you shall find good lodgings and merry hosts.†
Chpt 6
...this part of the ancient road was much more ruinous than any they had yet seen. They had to pick their way over great broken stones and between boulders and across rubble:
Chpt 7 *

ruinous = damaged
No doubt, if we'd had our minds on our job when we were at the Ruinous City, we'd have been shown how — found a little door, or a cave, or a tunnel, met someone to help us.†
Chpt 8
And, thank heavens, on the right side of the castle; the City Ruinous was in sight.†
Chpt 9
They now realized, too, that the road on which they were, and indeed all the ground between them and the City Ruinous, didn't offer as much cover as would hide a fox; it was all coarse grass and pebbles and flat stones.†
Chpt 9
The distance to the City Ruinous seemed longer than Jill would have believed possible.†
Chpt 9
"We had been told to look for a message on the stones of the City Ruinous," said Scrubb.†
Chpt 10

Definitions:

(1) (ruinous)
catastrophic or extremely harmful; or badly damaged or decayed (like ancient ruins)
(2) (meaning too rare to warrant focus)