Faith Undefined

Like many in the Church (and out of it no doubt) I have struggled to find a definition for faith that was both accurate and useful. I have been unable to do so in my few years on earth. In Boyd Petersen's biography of Hugh Nibley we read the following:

Faith is as difficult to define as it is to exercise. But for Hugh, that very difficulty makes it all the more real. "I have tried long and vainly to define faith to myself--for me that proves its reality, for we can rationalize and verbalize anything we please into existence, like lawyers, but faith can't be touched by the sophist and his tricks."