Time to restore confidence having lost one small gem (8)
I believe the answer is:
treasure
'gem' is the definition.
('treasure' can be a synonym of 'gem')
'time to restore confidence having lost one small' is the wordplay.
'time' becomes 't'.
'to restore confidence' becomes 'reassure' (I've seen this before).
'having lost' indicates named letters should be taken away.
'one small' becomes 's' (abbreviation - e.g. clothes size).
'reassure' with 's' removed is 'reasure'.
't'+'reasure'='TREASURE'
(Other definitions for treasure that I've seen before include "A quantity of valuable objects" , "Prize highly" , "Valuables, fortune" , "Set great store by" , "Accumulated wealth, might be buried" .)