Baby bear? (7)
'baby bear' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for cub that I've seen before include "Junior scout; puppy" , "eg Young lion" , "Young creature" , "Inexperienced reporter" , "Young one" .)
(Other definitions for gestate that I've seen before include "Develop (idea, foetus)" , "Evolve, ripen" , "Develop over time" , "Develop slowly" , "Carry in the womb" .)