thorn

[1]	barb , irritant , spine , spike , prickle , bristle , brier , bur/burr , point , bramble , cocklebur
[2]	thorn in (one's) side , spine , prickle , bother , irritation , pricker , sticker , annoyance , nuisance , spikelet , vexation , torment , torture , scourge , plague , affliction , irritant , bane , (Colloq) pain in the neck , (Colloq) (Slang) pain in the (Brit) arse/(US) ass