__ Major and Minor, constellations (4)
I believe the answer is:
ursa
'major and minor constellations' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ursa that I've seen before include "(and 11 across) Pole Star constellation" , "Constellation (Major or Minor)" , "and 18 Down: The Great Bear" , "__ Minor, the Little Bear" , "- Major, - Minor, prominent constellations" .)