Brief account unusual (8)
I believe the answer is:
acquaint
'brief' is the definition.
(I've seen this before)
'account unusual' is the wordplay.
'account' becomes 'ac' (abbreviation).
'unusual' becomes 'quaint' (quaint can mean unusual or quirky).
'ac'+'quaint'='ACQUAINT'
(Other definitions for acquaint that I've seen before include "Get familiar" , "Get to come to know" , "get up to date" , "Inform" , "Make aware or familiar with, say the facts" .)