'Sovereignty' is Latin for 'supreme authority' — the 'g' was falsely inserted by analogy with 'reign.'
Supreme power or authority, especially of a state to govern itself; the authority of a state to govern itself without external interference.
From Anglo-Norman 'sovereynete,' Old French 'souveraineté,' from 'souverain' (supreme in power, chief, highest), from Vulgar Latin *superānus (chief, principal, supreme — above all others), from Latin 'super' (above, over, beyond), from Proto-Indo-European *upér (over, above, beyond), a comparative of *upo (under, up from under). The PIE root *upo also produced Sanskrit 'upari' (above), Greek 'hyper' (over — as in 'hyperactive'), Latin 'super' (over — as in 'supernatural'), and Old English 'ofer' (over). The intrusive silent 'g' in the English spelling
The 'g' in 'sovereign' is a ghost letter — it was inserted in the fifteenth century by scribes who wrongly assumed the word was related to 'reign' (from Latin 'rēgnāre'). It is not. 'Sovereign' comes from Latin 'super' (above), while 'reign' comes from 'rēgnum' (kingdom). The false association was so natural — a sovereign is one