Length, extent (4)
I believe the answer is:
span
I believe this is a double definition.
'length' is the first definition.
(I know that span is a type of length)
'extent' is the second definition.
(I have seen 'Extent of 20 ' mean 'span' so perhaps 'extent' could also mean 'span')
(Other definitions for span that I've seen before include "Team of two matched oxen" , "Distance or interval between two points" , "Go across" , "Stretch; traverse" , "Extent - 9 inches" .)