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The Common Tone · Visual Language of Music
Half-Diminished (ø) A small circle crossed by a rising diagonal slash, set beside a chord letter.

Half-Diminished (ø)

also called: slashed circle · m7 flat 5 · half-diminished seventh

A small circle with a slash through it in a chord name (Bø7) meaning a half-diminished seventh chord — minor seventh with a lowered fifth.

What you do

Play a minor-seventh chord and lower its fifth a half step: root, minor third, diminished fifth, minor seventh. Bø7 = B–D–F–A. Many charts write the same chord as m7♭5 (Bm7♭5) — identical sound, different spelling on the page.

In context

Half-Diminished (ø) — example Two engraved measures, each holding the identical four-note chord. The first is labeled B half-diminished seven using the slashed-circle symbol; the second is labeled B minor seven flat five. Engraved by Verovio 6.2.1-8d42439 Bø7 Bm7b5
Two spellings, one sound: Bø7 and Bm7b5 both name the same four notes — B, D, F, A: a minor-seventh chord with its fifth lowered a half step. Which spelling a chart uses is house style.

Don’t confuse with

diminished-symbol
The PLAIN circle (B°7) is fully diminished — its seventh is lowered twice (double-flatted); the SLASHED circle (Bø7) keeps the ordinary minor seventh. One slash, one very different top note.

See also

diminished-symbol · chord-symbol-construction

For specialists

SMuFL: csymHalfDiminished
Record status: draft — verification pending (bookshelf locators + chord-symbol authority; OQ-1 blocks the slice gate)