Dropping off, like a casual acquaintance (7)
I believe the answer is:
nodding
'dropping off' is the definition.
(both can mean falling asleep)
'casual acquaintance' is the wordplay.
I cannot quite understand how this works, but
'casual' could be 'odd' (I've seen this before) and 'odd' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'like a' acts as a link.
Can you help me to learn more?
(Other definitions for nodding that I've seen before include "Like casual acquaintances" , "Not showing much interest in" , "Letting one's head drop" , "Indicating yes" , "Indicating agreement or recognition" .)