Synonyms for Sincere:

adj.

artless (adjective)
Unartful, open, Unbeguiling, downright, candid, plain, undisguised, artless, un-artificial, unrestrained, undeceptive, outgoing, overt, callow, undeceiving, honest, straightforward, naive, broad, frank, unsophisticated, Plain-spoken, direct, undeceitful, ingenuous, blunt, trusting, genuine, natural, uncalculating, unaffected.
direct (adjective)
undisguised.
enthusiastic (adjective)
fervent.
plainspoken (adjective)
Plain-spoken.
real (adjective)
concrete, authentic, tangible, actual, genuine, real, factual, honest, veritable, substantial, true, solid.
reputable (adjective)
honorable.
simple (adjective)
artless.
sobersided (adjective)
in earnest.
straightforward, honest (adjective)
serious, devout, natural, candid, faithful, frank, earnest, open, wholehearted, bona fide, true, trustworthy, heartfelt, unfeigned, actual, artless, forthright, plain, real, dear, unaffected, genuine.
truthful (adjective)
honorable, candid, earnest, ethical, straightforward, truthful, frank, factual, honest, trustworthy.

n.

fine, good, irreproachable, principled, upstanding, decent. unmannered, hearty. honest (noun)
forthright, reliable, faithful.
sincere (noun)
devout, honest, heart-whole, earnest, whole-souled, wholehearted, in earnest, heartfelt, cordial, genuine, bona fide, fervent, serious, unfeigned, true, solemn, dear.

Other synonyms:

forthright, unmannered, principled, reliable, upstanding, irreproachable, decent. fine. cordial
hearty, cordial.
loyal
faithful.

Usage examples for sincere

  1. I left the ship with sincere regret. – Autobiography of Andrew Carnegie by Andrew Carnegie