Admonish traveller also crossing border (9)
I believe the answer is:
reprimand
'admonish' is the definition.
(I've seen this before)
'traveller also crossing border' is the wordplay.
'traveller' becomes 'rep' (travel company worker).
'also' becomes 'and' (I've seen this before).
'crossing' means one lot of letters goes inside another.
'border' becomes 'rim' (I've seen this before**).
'rep'+'and'='repand'
'repand' enclosing 'rim' is 'REPRIMAND'.
(Other definitions for reprimand that I've seen before include "Tick off - carpet" , "Official scolding" , "Severe telling-off" , "talking-to" , "Formal censure" .)