(Christianity) The crown made of a thorny plant that Christ was forced to wear before his Crucifixion, in mocking reference to his alleged status as ‘king of the Jews’, or a representation of this.

(idiomatic) A persistent difficulty or something very annoying that will not go away.

plural of thorn apple

Datura spp., especially / Crataegus spp. / Solanum incanum, native to Africa and Asia

plural of thorn in someone's side

(figuratively) To enjoy a pleasant subject or thing, one must take trouble and hardship

Acacia luederitzii, a tree of Namibia.

plural of thorn-apple crystal

(medicine) An ammonium urate crystal having a rounded form with many projecting points.

(idiomatic) A persistent annoyance.