Substitute some tigers at zoo (6)
I believe the answer is:
ersatz
'substitute' is the definition.
('ersatz' can be a synonym of 'substitute')
'some tigers at zoo' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'ERSATZ' is hidden in the letters of 'tigers at zoo'.
(Other definitions for ersatz that I've seen before include "Made in imitation, from German" , "Phoney as in Germany" , "Artificial, imitation - from German" , "Imitation (from Ger.)" , "Substitute - fake" .)