Engineers disposed to be trustworthy (8)
I believe the answer is:
reliable
'be trustworthy' is the definition.
(similar in meaning)
'engineers disposed' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'disposed' becomes 'liable' (liable can mean likely or disposed to do something).
're'+'liable'='RELIABLE'
'to' acts as a link.
(Other definitions for reliable that I've seen before include "Can be depended upon, trustworthy" , "Trusty" , "Faithful" , "Unfailing" , "Dependable, trustworthy" .)