I. ˌcardinal ˈnumber BrE AmE ( also cardinal ) noun [countable]
a number such as 1, 2, or 3, that shows how many of something there are, but not what order they are in
⇨ ↑ ordinal number
II. car ‧ di ‧ nal 1 /ˈkɑːd ə nəl $ ˈkɑːr-/ BrE AmE noun [countable]
[ Date: 1100-1200 ; Language: Medieval Latin ; Origin: cardinalis , from Late Latin ( ⇨ ↑ cardinal 2 ); ]
[ Sense 2: Origin: from the color of a cardinal's clothing ]
1 . a priest of high rank in the Roman Catholic Church
2 . a North American bird. The male is a bright red colour.
3 . a ↑ cardinal number
III. cardinal 2 BrE AmE adjective [only before noun]
[ Date: 1200-1300 ; Language: Old French ; Origin: Late Latin cardinalis , from Latin cardo 'hinge' (= part that fastens something so that it can still move) ]
very important or basic SYN fundamental :
Having clean hands is one of the cardinal rules when preparing food.
an issue of cardinal importance