Uniform features of missile with air moving across it (12)
I believe the answer is:
similarities
'uniform features' is the definition.
(uniform or identical features)
'missile with air moving across it' is the wordplay.
'with' says to put letters next to each other.
'moving' indicates anagramming the letters.
'across' means one lot of letters goes inside another.
'missile' put after 'air' is 'airmissile'.
'airmissile' with letters rearranged gives 'similaries'.
'similaries' going around 'it' is 'SIMILARITIES'.
'of' is the link.
(Other definitions for similarities that I've seen before include "Resemblances" , "Parallels" , "things in agreement" .)