棘

thorns

stab

thorny (problem) / intractable

thistles and thorns / brambles / thorny undergrowth

ratchet

lit. to cut one's way through thistles and thorns (idiom) / fig. to overcome all obstacles on the way / to break through hardships / to blaze a new trail

sea-buckthorn

genus Hippophae / sea-buckthorns

coelacanth

lit. a path covered in brambles / a course of action beset by difficulties (idiom)

thorny problem / troublesome affair

echinoderm, the phylum containing sea urchins, sea cucumbers etc

Tsintaosaurus spinorhinus, a 10 meter long hadrosaur with a single horn on its duck-billed snout