Old British kind of cross (6)

I believe the answer is:

celtic

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'kind of cross' is the definition.

I cannot understand how the remainder of the clue works.

(Other definitions for celtic that I've seen before include "Scottish club" , "Roy Keane's team on the fringe" , "This tiger is credited with Irish prosperity" , "The Sea between southern Ireland and Cornwall" , "The sea between south Ireland and Cornwall" .)

I've seen this clue in The Globe and Mail.

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