More than one star which was once used to navigate (4)
I believe the answer is:
argo
This clue is a double definition.
'more than one star' is the first definition.
(Argo was historically considered a constellation)
'which was once used to navigate' is the second definition.
(ship in Greek myth)
(Other definitions for argo that I've seen before include "Old sailing vessel" , "Fabulous ship" , "Constellation; ship" , "Jason's vessel" , "Jason's craft" .)