undercurrent

noun

1 beware the dangerous undercurrents in the cove:

undertow, underflow, underswell, underdrift, understream, undertide, underrun;

Nautical underset;

rare underwork.

2 she sensed the undercurrent of despair in what he was saying:

undertone, overtone, suggestion, connotation, implication, intimation, hint, nuance, trace, suspicion, whisper, murmur, touch, tinge;

feeling, atmosphere, aura, tenor, echo, flavour, colouring, vein;

vibrations;

informal vibes;

rare subcurrent.

undercurrent Oxford Dictionary of English