Crossword puzzle clue "plays two notes simultaneously"

Plays two notes simultaneously

Voicings of simultaneously-sounded groups of musical notes in which the root note is not in the bass part

Its two halves can't run simultaneously

"Fancy" singer featured on "Problem" who in 2014 became the second ever to be simultaneously #1 and #2 with her first two hits: 2 wds.

Item in Schrödinger's box (and in this puzzle) that exists in two different states simultaneously

Novelist who had two spouses simultaneously

"I Want to Hold Your Hand" and "She Loves You" group who in 1964 became the first ever to be simultaneously #1 and #2 with their first two hits: 2 wds.

Where people take notes on notes