Warn a pretty girl about a Scotsman (8)
I believe the answer is:
admonish
'warn' is the definition.
(I know that warn can be written as admonish)
'a pretty girl about a scotsman' is the wordplay.
'pretty girl' becomes 'dish' (I've seen this in other clues).
'about' means one lot of letters goes inside another.
'a scotsman' becomes 'mon'.
'dish' enclosing 'mon' is 'dmonish'.
'a'+'dmonish'='ADMONISH'
(Other definitions for admonish that I've seen before include "Caution - reprimand" , "Reprove, warn" , "Chide or reprimand" , "Rebuke, tick off" , "Warn sternly" .)