Roy,
Well, you are correct that the use
of axioms in 20th century math and physics
involved matters far from obvious, but
from a history of thought perspective the
concept of an axiom does date back (at least?)
to Euclid, for whom they were assumptions
thought to be obvious from internal analysis,
even if later his axioms (or at least some
of them) came to be viewed as synthetic
propositions capable of empirical testing.
Barkley Rosser