Lacking confidence, shy (7)
I believe the answer is:
bashful
I believe this clue is a double definition.
'lacking confidence' is the first definition.
(I've seen this before)
'shy' is the second definition.
(I've seen this in another clue)
(Other definitions for bashful that I've seen before include "Coy" , "Neither Happy, Sneezy, Dopey, Grumpy, Sleepy nor Doc!" , "Shy, timid" , "One of Disney's dwarves" , "Shy, easily embarrassed" .)