刺客 means a thug or thugs.  刺 (shi) means to stab. 客(kyaku) means a visitor. So it means someone who comes to kill you. I thought the pronunciation was “shikyaku” but when I referred to a web dictionary, I found that Shikaku is right but now many Japanese actually use Shikyaku as well. So, may be both are fine.

最近よく耳にする「刺客」は、「しかく」と読むと思っていたのに、政治家の中には「しきゃく」と言っている人もいます。どちらが正しいのですか？ http://kanjibunka.com/kanji-faq/old-faq/q0338/

「刺客」は「しきゃく」？「しかく」？ http://aslan-bun.com/?p=736