proponent(n = noun.person) advocate, advocator, exponent - a person who pleads for a cause or propounds an idea;
is a kind of individual, mortal, person, somebody, someone, soul
has particulars: apologist, justifier, vindicator, constitutionalist, darwinian, democrat, populist, federalist, gnostic, humanist, humanitarian, ideologist, ideologue, internationalist, irredentist, irridentist, isolationist, jansenist, libertarian, maoist, marxist, nationalist, neoclassicist, neutralist, nullifier, drumbeater, partisan, zealot, partitionist, platonist, pro-lifer, presenter, sponsor, protectionist, republican, ritualist, ruralist, secessionist, secularist, separationist, separatist, interpreter, representative, spokesperson, voice, suffragist, admirer, booster, champion, friend, protagonist, supporter, supremacist, teleologist, thatcherite, unilateralist
Derived form verb propound₁

   Making proposals; proposing. [1913 Webster]

1.  One who makes a proposal, or lays down a proposition. Dryden. [1913 Webster]

2.  The propounder of a thing. [1913 Webster]

proponent, n. & adj.
--n. a person advocating a motion, theory, or proposal.
--adj. proposing or advocating a theory etc.

Etymology:
L proponere (as PROPOUND)