one who forms opinions on the basis of reason independently of authority; especially : one who doubts or denies religious dogma
The question presents something of a dilemma for me. Instinctively, or perhaps more accurately – reflexively- I would answer in the negative. But to do so would likely be erroneous.
Christians who can isolate/segment belief in God, but do not permit it to supplant their ability to accept scientific evidence for evolutionary theory; who do not re-write history in favor of a "Christian nation," where no such historical support exists; who do not bastardize the meaning of the 1st amendment's Establishment Clause; or do not invoke God or the Bible to justify religious involvement in America's policies, laws, waging war, nor allow their religious belief to impede people's reproductive rights or pursuit of happiness based on sexual preference or gender; and who recognize and support Jefferson's intent for the Separation of Church and State; then my answer is YES, one can be both a Xtian and Freethinker.
The Rev Barry Lynn, Director of Americans United for the Separation. of Church and State is one of those. I have come to realize there are many like him.
But if a Xtian would require me to give objective evidence, irrefutable proof, for my claim that I have a monkey that recites Shakespeare, but requires no such proof that a snake talked and the first human was formed from mud by a super being, then they have accepted tradition, dogma, religious authority over reason and cannot be called a freethinker. A freethinker requires proof, objective evidence of something incredible proffered as fact, and applies that premise consistently.
If one rejects volumes of scientific data corroborated by multiple disciplines all of which point to evolution to explain origin of species; but accept a myth written by pre-scientific nomadic cultists to explain why species exist... he rejects freethought.
If one believes prayer has efficacy and can influence a supreme beings decision making for his life, or the planet, or their dog, in spite of overwhelming evidence to the contrary through many controlled studies, accepting instead the dictates of the Bible and the anecdotal stories of like minded believers... they cannot be a freethinker.
If ones attributes certain outcomes to divine intervention (the most complex if all potential explanations), as oppose to natural physical laws and /or coincidence / probability as the causal factor, they defy freethinking.
If one believes morality and ethics are determined by a supreme being and not the result of culture and the evolution of civilization as a natural outgrowth for the need for a cohesive and cooperative society, you can’t be called freethinker.
The things I mentioned are not meant to be a definitive listing of what determines if a person is or isn’t a freethinker. There is no definitive list. These aren't any ones rules for joining the community of free thought. We don’t have rules. They aren't a doctrine or directive from some hierarchy of freethinkers. We don’t have a doctrine or hierarchy. They represent my strictly my perspective. But, I expect they would likely be agreed to by many freethinkers. And note that the definition of freethinker says “especially” those who doubt or deny religious dogma...not “exclusively” those who doubt or deny it.
Then again, maybe I'm wrong. I'm open to being convinced otherwise by reason. After all, I am a freethinker.