Fitting program on old web page (8)
I believe the answer is:
apposite
'fitting' is the definition.
(apposite means suitable or appropriate)
'program on old web page' is the wordplay.
'program' becomes 'app' (type of computer program).
'on' means one lot of letters go next to another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'web page' becomes 'site' (website).
'app'+'o'+'site'='APPOSITE'
(Other definitions for apposite that I've seen before include "Appropriate for purpose or occasion" , "fitting" , "Appropriate, pertinent" , "Suited for the purpose" , "Suitable, relevant" .)