undercurrent

noun

1. 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.
2. a current, as of air or water, that flows below the upper currents or surface.

noun

1. a current that is not apparent at the surface or lies beneath another current
2. an opinion, emotion, etc, lying beneath apparent feeling or meaning

n.1660s, “stream of water or air flowing beneath the surface or beneath another current,” a hybrid formed from under + current (n.). The figurative sense of “suppressed or underlying character” is attested from 1817.