trilling

noun3

1. •
   The production of a trill sound.

   • During the singing act these wing surfaces are moved rapidly on each other, producing the familiar strident trillings of midsummer. — 1910
2. •
   A compound crystal consisting of three individuals.

   • Diametrically opposed rays of these stellate groups are of the same optical orientation and the twins are, therefore, trillings ( fig. 29 ). — 1966
3. •
   (no longer used, rare) One of three offspring born at the same birth; a triplet.

   • Every 67th lying-in woman has twins, every 5333rd has trillings, and only every 150,000th has fourlings. — 1842