Increasing concern primarily about going to Cologne (8)
I believe the answer is:
crescent
'increasing' is the definition.
(thesaurus)
'concern primarily about going to cologne' is the wordplay.
'primarily' says to take the initial letters.
'about' becomes 're' (regarding).
'going to' says to put letters next to each other.
'cologne' becomes 'scent' (cologne is a type of scent).
The initial letter of 'concern' is 'c'.
'c'+'re'+'scent'='CRESCENT'
(Other definitions for crescent that I've seen before include "looking sickly" , "Waxing process could show one" , "Shape of moon in first or last quarter" , "Young-moon shape" , "Semi-circular shape" .)