Accompanying strain; subordinate and underlying meaning; accompaniment; undertone. "In the very (poetry) there often an undersong of sense which none beside the poetic mind... can comprehend."
... Vision of Life entreats those eyes Where stars of glamour mock at revelations. But singular fiery moments do surprise With dreadful or delicious divinations The whorls of our blue Labyrinth: the sweet Blind sense of touch tells like an undersong Marvellous matters. What though snared feet, And wounded hands, and ravelled coils of wrong, Plead that the solemn Vision might make whole Our imperfection?—Fevered second-sight, Audacious wisdom of the blinded soul, Dim delicate auroras of delight That thrill ... — The Hours of Fiammetta - A Sonnet Sequence • Rachel Annand Taylor