We don't have synonyms for air defence yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are air defense and air-defence.
(n) :
Alternative spelling of air defense. [(military, weaponry) The use of systems, equipment, and personnel to prevent or reduce the impact of an attack by enemy aircraft or missiles.]
(n) :
Alternative spelling of air defense. [(military, weaponry) The use of systems, equipment, and personnel to prevent or reduce the impact of an attack by enemy aircraft or missiles.]