Officer carrying bladed tools is most careless (6)
I believe the answer is:
laxest
'most careless' is the definition.
('lax' can be a synonym of 'careless')
'officer carrying bladed tools' is the wordplay.
'officer' becomes 'lt' (abbreviation for lieutenant).
'carrying' indicates putting letters inside.
'bladed tools' becomes 'axes' (axe is a kind of tool. I am not sure about the 'bladed' bit.).
'lt' going around 'axes' is 'LAXEST'.
'is' acts as a link.
Can you help me to learn more?
(Another definition for laxest that I've seen is " not tight in the least".)