un ‧ der ‧ tone /ˈʌndətəʊn $ -dərtoʊn/ BrE AmE noun [countable]
1 . a feeling or quality that is not directly expressed but can still be recognized ⇨ overtone
undertone of
There was an undertone of sadness in her letter.
Opponents claim the policy has racist undertones.
2 . literary if you speak in an undertone, you speak quietly
in an undertone
‘Don’t be too upset if he doesn’t come,’ said Drew in an undertone.