In close proximity (4,2,4)
'in close proximity' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for cheek by jowl that I've seen before include "In immediate proximity" , "closely linked" , "Side by side, close" , "Close together" , "In close proximity" .)
(Other definitions for side by side that I've seen before include "Next to each other" , "Close together, abreast" , "In tandem" , "Level" , "As partners" .)