Brewer's: Cheek by Jowl
In intimate confabulation; tête-á-tête. Cheek is the Anglo-Saxon ceca, céac-bán, cheek-bone; and jowl is the Anglo-Saxon ceole (the jaw); Irish, gial.
“Ill go with thee, cheek by jowl.” —Shakespeare: Midsummer Night's Dream, iii. 2.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894