One who devotes much time to thought or meditation.(noun)
One who thinks or reasons in a certain way: a careful thinker. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "thinker" in a sentence
"A sign of a low-quality thinker is the use of "What about X?", where X is any hot topic."
"From there iterative repetition refines the question until the critical thinker is able to reach a conclusion. chunkdz: Why don't ID'ers publish research in scientific journals?"
"For a dishonest thinker is under no moral obligation to accept a conclusion to which his logic drives him; even if he loses the argument, a dishonest thinker is not under a duty to change his mind or mend his ways."