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Webster 1913 Edition

Adj.

[L.

spinescens

-entis

, p. pr. of

spinescere

to know to grow thorny, fr.

spina

a thorn: cf. F.

spinescent

(Bot.)

Becoming hard and thorny; tapering gradually to a rigid, leafless point; armed with spines.

Gray.

Adj.

[from spine.] Becoming hard and thorny.

spinescent ‎(not comparable)

This does not refer to spine in the sense of a backbone or book binding, but in the sense of "spiny". Cacti and sea urchins are spinescent.