underscent

plural underscents

1. A scent that is perceptible but less prominent than other scents in a particular environment.

   1902, Marie Corelli, “Temporal Power”: A Study in Supremacy, London: Methuen, Chapter 18, p. 256, The under-scent of hidden violets among moss flowed potently upon the quiet air, mingled with strong pine-odours and the salt breath of the gently heaving sea,

   3 more examples

   […] below her perfume lingered another perfume, more elusive, more aggressive, a man’s scent. Still staring into her eyes, he deliberately blanked his mind three times; and each time the first picture triggered in his mind by that underscent was the face of Billy Merganser.

   1968, M. K. Joseph, chapter 4, in The Hole in the Zero,, New York: Dutton, page 67

   […] night is when the ground heaves up the distracting odours of burrowed life: catfish and reptiles, and the musk of regeneration in scorched roots. [footnote:] Known as underscents, these odours hover beneath the buoyant smells of dung, leaves, living animals and even slaughter.

   1999, Barbara Gowdy, chapter 8, in The White Bone, New York: Picador, page 127

   hermetically enclosed rooms that had the persistent, unpleasant underscent of chemicals

   2013, Richard Flanagan, The Narrow Road to the Deep North, London: Vintage, published 2014, page 402