Engineer agreed to maintain whiskey plant (7)
I believe the answer is:
ragweed
'plant' is the definition.
The answer is an example.
'engineer agreed to maintain whiskey' is the wordplay.
'engineer' indicates an anagram.
'to maintain' is an insertion indicator (maintain can mean to keep or preserve).
'whiskey' becomes 'W' (alpha bravo charlie delta ...).
'agreed' anagrammed gives 'rageed'.
'rageed' going around 'w' is 'RAGWEED'.
(Other definitions for ragweed that I've seen before include "Plant of daisy family" , "Threat to horses" , "Unwanted plant with yellow flowers" , "Allergenic plant" , "bloomer" .)