We don't have synonyms for cos lettuce yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are cos lettuces.
(n) :
(chiefly UK) Synonym of romaine lettuce, a long-leaved variety of lettuce.
(n) :
(chiefly UK) Alternative letter-case form of cos lettuce, romaine lettuce. [(chiefly UK) Synonym of romaine lettuce, a long-leaved variety of lettuce.]
(n) :
(chiefly UK) Synonym of romaine lettuce, a long-leaved variety of lettuce.
(n) :
(chiefly UK) Alternative letter-case form of cos lettuce, romaine lettuce. [(chiefly UK) Synonym of romaine lettuce, a long-leaved variety of lettuce.]