Very busy, that man, tense, collared by military boss (6)
I believe the answer is:
hectic
'very busy' is the definition.
(I've seen this before)
'man tense collared by military boss' is the wordplay.
'man' becomes 'he' (he refers to a man).
'tense' becomes 't' (abbreviation used in many dictionaries).
'collared by' indicates putting letters inside (I've seen this in other clues).
'military boss' becomes 'CIC' (commander in chief).
't' inserted into 'cic' is 'ctic'.
'he'+'ctic'='HECTIC'
'that' acts as a link.
(Other definitions for hectic that I've seen before include "'Rushed, madly busy (6)'" , "Frantic, busy" , "Agitated and rushed" , "Marked by intense activity" , "Frantically active" .)