High-ranking officer dismissing line in groups (6)
I believe the answer is:
genera
'in groups' is the definition.
'genera' can be an answer for 'groups' (I've seen this before). I am not sure about the 'in' bit.
'high-ranking officer dismissing line' is the wordplay.
'high ranking officer' becomes 'general' (I've seen this before).
'dismissing' indicates named letters should be taken away.
'line' becomes 'l'.
'general' with 'l' taken out is 'GENERA'.
Can you help me to learn more?
(Other definitions for genera that I've seen before include "classes" , "Blood vessel" , "Types" , "Categories making up a family" , "Biological groups" .)