a tendency underlying or at variance with the obvious or superficial significance of words, actions, etc.

Even in his friendliest remarks, one could sense an undercurrent of hostility.

a current, as of air or water, that flows below the upper currents or surface.

noun

atmosphere , aura , crosscurrent , direction , eddy , feeling , flavor , hint , inclination , indication , insinuation , intimation , murmur , overtone , propensity , riptide , sense , suggestion , tendency , tenor , tinge , trace , trend , underflow , undertone , undertow , vibes , vibrations , implication , inkling , suspicion , drift , mood