Old Tuareg reeling in shock (7)
I believe the answer is:
outrage
'shock' is the definition.
(I know that shock can be written as outrage)
'old tuareg reeling in' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'reeling' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'tuareg' with letters rearranged gives 'utrage'.
'o' inserted within 'utrage' is 'OUTRAGE'.
(Other definitions for outrage that I've seen before include "furious reaction" , "Shock grossly" , "Barbarity" , "Scandal" , "Very angry reaction" .)