Unusual kind of gate that Lamba went back around (8)
I believe the answer is:
abnormal
'unusual' is the definition.
(similar in meaning)
'kind of gate that lamba went back around' is the wordplay.
'kind of gate' becomes 'nor' (I can't justify this - if you can you should give a lot more credence to this answer).
'that lamba' becomes 'lamba'.
'went back' says the letters should be written backwards.
'around' means one lot of letters goes inside another.
'lamba' reversed gives 'abmal'.
'nor' put within 'abmal' is 'ABNORMAL'.
Can you help me to learn more?
(Other definitions for abnormal that I've seen before include "Non-standard" , "Deviating from the standard" , "Deviating from the usual" , "Freakish" , "Odd" .)