Bard is one press-ganged by Lieutenant for frontier (5)
I believe the answer is:
limit
'for frontier' is the definition.
(I've seen this before)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for limit that I've seen before include "Keep in" , "Cap" , "Extreme point" , "Confine within bounds" , "Restrict - term" .)