A cold calm way to disappear? (7)
I believe the answer is:
illness
'a cold' is the definition.
(a cold is a type of illness)
'calm way to disappear?' is the wordplay.
'calm' becomes 'stillness' (being still is being calm).
'way' becomes 'st' (abbreviation for street).
'to disappear?' suggests deleting specific letters.
'stillness' with 'st' taken out is 'ILLNESS'.
(Other definitions for illness that I've seen before include "Disease, sickness" , "Ailment, disorder" , "suffering this" , "Period of sickness" , "Indisposition, sickness" .)