敵わない[kanawanai] no match for
怨敵[onteki] sworn enemy
外敵[gaiteki] foreign enemy
敵う[kanau] to come true (wish)
仇敵[kyuuteki] bitter enemy

敵討[katakiuchi] vengeance
敵同士[tekidoushi] mutual enemies
旧敵[kyuuteki] old enemy
強敵[kyouteki] formidable enemy
公敵[kouteki] public enemy

仇討[adauchi] vengeance
かたき討ち[katakiuchi] vengeance
討つ[utsu] to shoot (at)
検討[kentou] consideration
検討委員会[kentouiinkai] investigative commission

再検討[saikentou] re-examination
剿討[soutou] cleaning up
相討ち[aiuchi] simultaneously striking one another (in kendo, etc.)
尊王討幕[sonnoutoubaku] reverence for the emperor and the overthrow of the shogunate
討ち破る[uchiyaburu] to break