Period austere with skill shortage (4)

I believe the answer is:

span

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'period' is the definition.
(span is a kind of period)

I don't understand how the remainder of the clue works.

(Other definitions for span that I've seen before include "Bridge - spick and ___" , "Distance between two points in time or place" , "Length of bridge - 9 inches!" , "Steeleye ___ , British folk-rock band, formed 1969" , "Distance between bridge abutments" .)

I've seen this clue in The Independent.

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