Eccentric aunt carrying type of bomb in both hands — it's normal (7)
I believe the answer is:
'it's normal' is the definition.
(similar in meaning)
'eccentric aunt carrying type of bomb in both hands' is the wordplay.
'eccentric' is an anagram indicator.
'carrying' is a charade indicator (letters next to each other) (in a down clue, the bottom letters carry others).
'type of bomb' becomes 'A' (A-bomb,atom bomb).
'in' means one lot of letters goes inside another.
'both hands' becomes 'RL' (abbreviation for left and right).
'a' placed within 'rl' is 'ral'.
'aunt' with letters rearranged gives 'natu'.
(Other definitions for natural that I've seen before include "as one might expect" , "Ordinary" , "Normal; not man-made" , "in a pack, not wild?" , "Illegitimate" .)