defence
noun
1 the defence of fortresses against enemies:
protection, shielding, safeguarding, guarding;
security, fortification, cover, shelter, screen, resistance, deterrent.
2 the enemy's defences were sited all along the ridge:
barricade, fortification, bulwark, buttress, fortress, fastness, keep, rampart, outpost, bastion.
3 he planned to speak in defence of his old chief:
vindication, justification, support, advocacy, approval, endorsement, promotion;
apology, apologia, explanation, explication, excuse, extenuation, exoneration, palliation.
defence Oxford Dictionary of English