'arraignable' is formed in Modern English by adding the adjective-forming suffix '-able' to the verb 'arraign'; the suffix '-able' ultimately comes from Latin '-abilis' via Old French '-able', meaning 'able to be'.

The verb 'arraign' entered English from Anglo-Norman/Old French (forms such as 'areignier'/'araignier') and appeared in Middle English as forms like 'arraignen' or 'arreyne'; the adjective was later produced by combining this verb with the productive English suffix '-able'.

Originally the verb meant 'to call before a court or reproach formally'; the adjective formed from it has retained the core sense of 'able to be called before a court' and remains close to that original meaning.