Accountant sent up American associate in a thoughtless way, perhaps (8)
I believe the answer is:
casually
'a thoughtless way perhaps' is the definition.
I can't judge whether this defines the answer.
'accountant sent up american associate' is the wordplay.
'accountant' becomes 'CA' (abbreviation for chartered accountant).
'sent up' says the letters should be written in reverse.
'american' becomes 'US' (United States).
'associate' becomes 'ally' (ally is a kind of associate).
'us' written backwards gives 'su'.
'ca'+'su'+'ally'='CASUALLY'
'in' is the link.
Can you help me to learn more?
(Other definitions for casually that I've seen before include "Nonchalantly" , "In an unconcerned manner" , "In an off-hand manner" , "In a relaxed manner" .)