Distance spanned by mountain chain (4)
I believe the answer is:
inch
'distance' is the definition.
(I have seen 'Short distance' mean 'inch' so perhaps 'distance' could also mean 'inch')
'spanned by mountain chain' is the wordplay.
'spanned by' indicates a hidden word (the words cover up or span the hidden answer).
'INCH' can be found hidden inside 'mountain chain'.
(Other definitions for inch that I've seen before include "Creep towards < island" , "Short measure; island" , "Not very far" , "2.54cm" , "amount of rainfall?" .)