Lockbearer

" 'To Gimli son of Glóin', she said, 'give his Lady's greeting. Lockbearer, wherever thou goest my thought goes with thee. But have a care to lay thine axe to the right tree!' "

― Gandalf passing on Galadriel's message

Lockbearer was the name that Galadriel used of Gimli in her message delivered by Gandalf in the Fangorn Forest, so chosen because Galadriel had given three golden strands of her hair to Gimli as a farewell present (at his request) in Lothlórien.