I have nothing to back up ""senior" but compare such titles as "senior principal" in the UK civil service

senior
adjective

1.
of or for older or more experienced people.
"senior citizens"
h
Similar:
older

elder
more grown up
h
Opposite:
junior
younger

British
for or denoting schoolchildren above a certain age, typically 11.
"the senior girls play badminton while the others play hockey"
US
of or for the final year at a university or high school.
relating to or denoting competitors of above a certain age or of the highest status in a particular sport.
"McCluskey made an instant impact on his senior debut"
(in names) denoting the elder of two who have the same name in a family, especially a father as distinct from his son.
adjective: Senior
"Henry James senior"
h
Similar:
the Elder

major
I

(the First)

2.
high or higher in rank or status.
"he is a senior Finance Ministry official"
h
Similar:
higher-ranking
highest-ranking
high-ranking
superior
top
chief
more/most important
high-status
ranking
h
Opposite:
junior

subordinate

noun
noun: senior; plural noun: seniors

a person who is a specified number of years older than someone else.
"she was only two years his senior"

A prefect (French: préfet, plural préfets) in France is the state's representative in a department or region. Subprefects (French: sous-préfets) are responsible for the subdivisions of departments, known as arrondissements. The office of a prefect is known as a prefecture and that of a subprefect as a subprefecture. Regional prefects are ex officio the departmental prefects of the regional prefecture.

Prefects are tasked with upholding the law in the department they serve in, including controlling the actions of local authorities to ensure adhesion to national guidelines. They are authorised to sue local collectivities in the name of the state.[1]

Prefects are appointed by a decree of the President of France when presiding the Government's Council of Ministers, following a proposal by the Prime Minister and the Minister of the Interior.[2] They serve at the Government's discretion and can be replaced at any meeting of the Council of Ministers.

From 1982 to 1988, under the Socialist administration of President François Mitterrand, prefects were called commissaires de la République (the Republic's commissioners) and subprefects commissaires adjoints de la République (the Republic's deputy commissioners).[3]