Laconic beat box? Just the reverse! (7)
I believe the answer is:
spartan
'laconic' is the definition.
(I've seen this in another clue)
'beat box? just the reverse' is the wordplay.
I cannot quite see how this works, but
'beat' could be 'tan' (tan can mean to beat or hit) and 'tan' is found in the answer.
'box?' could be 'spar' (spar can mean to box) and 'spar' is found in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for spartan that I've seen before include "Austere - disciplined" , "toughly-disciplined type" , "Not comfortable" , "Ascetic - ancient Greek" , "Indifferent to comfort" .)