1. [adj]  firm and dependable especially in loyalty; "a steadfast ally"; "a staunch defender of free speech"; "unswerving devotion"; "unswerving allegiance"
2. [adj]  going directly ahead from one point to another without veering or turning aside; "some people see evolution as an undeviating upward march from simple organisms to the very complex"; "a straight and narrow tree-lined road unswerving across the lowlands"

UNSWERVING is a 10 letter word that starts with U.