Small nuclear missile might be loud (8)
I believe the answer is:
strident
'loud' is the definition.
(strident can mean harsh-sounding or loud)
'small nuclear missile' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'nuclear missile' becomes 'Trident' (UK nuclear weapons system).
's'+'trident'='STRIDENT'
'might be' is the link.
(Other definitions for strident that I've seen before include "Offensively loud and harsh" , "giving views forcefully" , "Noisy" , "ear-piercing" , "Loud and vociferous" .)