Forward and backward in trepidation (4)
I believe the answer is:
pert
'forward' is the definition.
(both can mean cheeky or disrespectful)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for pert that I've seen before include "Saucy and impudent" , "Impudent, cheeky" , "Saucy and chipper" , "Irreverent or saucy" , "It's fresh" .)