Reassurance initially found in a competitor's appearance (7)
I believe the answer is:
arrival
'appearance' is the definition.
(I've seen this before)
'reassurance initially found in a competitor's' is the wordplay.
'initially' suggests taking the first letters.
'found in' indicates putting letters inside.
'competitor' becomes 'rival' ('rival' can be a synonym of 'competitor'**).
The initial letter of 'reassurance' is 'r'.
'a'+'rival'='arival'
'r' inserted within 'arival' is 'ARRIVAL'.
(Other definitions for arrival that I've seen before include "Someone who's just come" , "Entry" , "Act of coming" , "The A in ETA" , "Attainment of destination" .)