Carry back in, terribly late though sober (8)
I believe the answer is:
teetotal
'sober' is the definition.
(similar in meaning)
'carry back in terribly late' is the wordplay.
'carry' becomes 'tote' (toting is a kind of carrying).
'back' says the letters should be written in reverse.
'in' indicates putting letters inside.
'terribly' indicates an anagram.
'tote' in reverse letter order is 'etot'.
'late' with letters rearranged gives 'teal'.
'etot' placed inside 'teal' is 'TEETOTAL'.
'though' is the link.
(Other definitions for teetotal that I've seen before include "Completely abstaining from alcoholic drink" , "avoiding any possibility of inebriation" , "Abstaining completely from alcohol" , "Sober" , "Pledged to abstain from alcohol" .)