Titan who held up the sky (5)
I believe the answer is:
atlas
'titan who held up the sky' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for atlas that I've seen before include "Giant" , "A geog. book; N. African range" , "Collection of maps" , "N. African mountains; a Titan" , "God" .)