Mysterious meteoroid oddly missing base (5)
I believe the answer is:
eerie
'mysterious' is the definition.
(I've seen this in another clue)
'meteoroid oddly missing base' is the wordplay.
'oddly missing' means one should take alternating letters.
'base' becomes 'e' (Euler's number - base of natural logarithms).
The alternating letters of 'meteoroid' are 'eeri'.
'eeri'+'e'='EERIE'
(Other definitions for eerie that I've seen before include "Unnerving" , "Weird, uncanny" , "Bloodcurdling" , "Spooky, weird" , "Unnatural" .)