Company in train sadly cold and inducing sleep (8)
I believe the answer is:
narcotic
'inducing sleep' is the definition.
'company in train sadly cold' is the wordplay.
'company' becomes 'co' (abbreviation).
'in' means one lot of letters goes inside another.
'sadly' is an anagram indicator.
'cold' becomes 'c' (eg on taps).
'train' is an anagram of 'narti'.
'co' put within 'narti' is 'narcoti'.
'narcoti'+'c'='NARCOTIC'
'and' is the link.
(Other definitions for narcotic that I've seen before include "A sleep-inducing drug" , "Drug producing torpor" , "Drug producing numbness and stupor" , "Drug that produces numbness or stupor" , "Sedative" .)