Keep demonstrating reticence (7)
I believe the answer is:
reserve
This clue is a double definition.
'keep' is the first definition.
(reserving is a kind of keeping)
'reticence' is the second definition.
(synonyms)
'demonstrating' is the link.
(Other definitions for reserve that I've seen before include "Modesty- store" , "Reticence" , "not in the front line" , "Conservation area" , "Wine kept" .)