I. truer
comparative of true
II. tru·er ˈtrüə(r); -u̇(ə)r, -u̇ə noun
( -s )
Etymology: true (III) + -er
: one that trues: as
a. : a device for trueing abrasive wheels
b. : one that trues objects (as optical lenses, green clay blocks, or springs) to bring them into correct condition, size, or alignment