The Collaborative International Dictionary of English v.0.48:
Tiers 'etat \Tiers` ['e]`tat"\ [F.]
The third estate, or commonalty, in France, answering to the
commons in Great Britain; -- so called in distinction from,
and as inferior to, the nobles and clergy.
Note: The refusal of the clergy and nobility to give the
tiers ['e]tat a representation in the States-general
proportioned to their actual numbers had an important
influence in bringing on the French Revolution of 1789.
Since that time the term has been purely historical.