(undertones)
1.
If you say something in an undertone, you say it very quietly.
'What d'you think?' she asked in an undertone...
Well-dressed clients were talking in polite undertones as they ate.
N-COUNT: in N
2.
If something has undertones of a particular kind, it suggests ideas or attitudes of this kind without expressing them directly.
...a witty, racy story with surprisingly serious undertones.
N-COUNT: with supp