undertone

noun

1 he said something in an undertone to the woman at his side:

low voice, murmur, whisper, mutter;

low tones, hushed tones.

▷antonyms shout.

2 she was deeply affected by the story's dark undertones:

undercurrent, hint, overtone, suggestion;

connotation, nuance, intimation, inkling, insinuation, implication, trace, suspicion, tinge, touch, vein, breath, whiff, whisper, glimmer, atmosphere, aura, tenor, flavor, coloring, shade, smack;

rare subcurrent.