Unusually considerate and lacking something mysterious (8)
I believe the answer is:
esoteric
'mysterious' is the definition.
(similar in meaning)
'unusually considerate and lacking' is the wordplay.
'unusually' indicates an anagram.
'lacking' indicates named letters should be taken away.
'considerate' with 'and' taken out is 'cosierte'.
'cosierte' with letters rearranged gives 'ESOTERIC'.
'something' is the link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for esoteric that I've seen before include "just seen by specialist" , "Understandable by only an enlightened inner circle" , "Highly specialised" , "Occult" , "Hard to understand" .)