A new pupil.
A low state of the physical faculties.
A pale colour, or one seen underneath another colour.
An implicit message perceived subtly alongside, but not detracting noticeably from, the explicit message conveyed in or by a book, film, verbal dialogue or similar (contrast with overtone); an undercurrent.
An auditory tone of low pitch or volume.
To accompany as an undertone.
To say or speak in an undertone.
To present as less important, noticeable or prominent.