This subsection lists the definitions from Book 4 of "Euclid’s Elements". Euclid’s definitions avoid figures. At BookOfProofs, figures are given for the most definitions.

- Definition: 4.1: Rectilinear Figure Inscribed in Another Rectilinear Figure
- Definition: 4.2: Rectilinear Figure Circumscribed about Another Rectilinear Figure
- Definition: 4.3: Inscribing Rectilinear Figures in Circles
- Definition: 4.4: Circumscribing Rectilinear Figures about Circles
- Definition: 4.7: Chord and Secant
- Definition: 4.6: Circumscribing Circles about Rectilinear Figures
- Definition: 4.5: Inscribing Circles in Rectilinear Figures

**Callahan, Daniel**: "Euclid’s 'Elements' Redux" 2014**Prime.mover and others**: "Pr∞fWiki", https://proofwiki.org/wiki/Main_Page, 2016

**Health L. Thomas (Transl.)**: "Euclid's Elements - all thirteen books", Green Lion Press, 2013,