Box secreted by Mexican is terrifying (8)
I believe the answer is:
canister
'box' is the definition.
(I've seen this before)
'secreted by mexican is terrifying' is the wordplay.
'secreted by' indicates a hidden word.
'CANISTER' can be found hidden inside 'mexican is terrifying'.
(Other definitions for canister that I've seen before include "Storage container, for tea say" , "Metal box" , "Container for e.g. tea" , "Jar (of e.g. tea, sugar)" , "Metal case" .)