1. the quality of being true, genuine, actual, or factual: the truth of his statement was attested
2. something that is true as opposed to false: you did not tell me the truth
3. a proven or verified principle or statement; fact: the truths of astronomy
4. ( usually plural ) a system of concepts purporting to represent some aspect of the world: the truths of ancient religions
5. fidelity to a required standard or law
6. faithful reproduction or portrayal: the truth of a portrait
7. an obvious fact; truism; platitude
8. honesty, reliability, or veracity: the truth of her nature
9. accuracy, as in the setting, adjustment, or position of something, such as a mechanical instrument
10. the state or quality of being faithful; allegiance
fact, veracity, sincerity, candor, frankness, precision, exactness.
In the first chapter of the Book of Mormon, Nephi defined true as being consistent with personal experience.
I like the definition that means "pointed in the right direction" - as with "true north".
In a fireside at BYU in November 2009, President Uchtdorf said:
Because we see imperfectly in mortality, not everything is going to make sense right now. … It’s true that ‘faith is not … a perfect knowledge’ (Alma 32:21), but as you exercise your faith, applying gospel principles every day under any circumstances, you will taste the sweet fruits of the gospel, and by this fruit you will know of its truth. (“The Reflection in the Water”)
In this quote, he used "truth" in reference to "the gospel" - so he wasn't even talking about "the Church" in that passage. That is a critical distinction to make when evaluating his talk and asking what he meant. "The Gospel" is defined properly, in my opinion, quite narrowly as one of two things:
1) the principles and/or commandments that Jesus taught;
2) faith, repentance, baptism, the gift of the Holy Ghost and enduring to the end.
About the only way that "truth" can apply within that context is if it is focused on the eventual outcomes being what are claimed. There is no way to try to define it as anything related to "accurate in a quantifiable way" with that usage - and faith is all we have in that regard, since even Jesus promised trial and pain to those who followed him most closely. Thus, Elder Uchtdorf was 100% correct. The only way to "know" is through faith (and it requires faith to even believe that knowledge might be possible eventually).