1. In very close physical proximity, crowded together.
   • 1603, Michel de Montaigne, chapter 17, in John Florio, transl., The Essayes, […], book II, printed at London: By Val[entine] Simmes for Edward Blount […], OCLC 946730821 ↗:

     Wee see Merchants, countrey-Justices, and Artificers to march cheeke by joll with our Nobilitie, in valour, and militarie discipline.

   • 2012, Helen Pidd, The Guardian, 8 April:

     he had made his peace with the idea of spending half-term cheek-by-jowl on a cruise ship with the world's biggest Titanic enthusiasts.

2. (by extension) In very close or intimate association.

cheek by jowl

1. Tightly packed.

• French: joue contre joue, côte à côte