Saw house in Paris designed by Frenchman (8)
I believe the answer is:
aphorism
'saw' is the definition.
(I've seen this before)
'house in paris designed by frenchman' is the wordplay.
'house' becomes 'ho' (abbreviation for house).
'in' indicates putting letters inside.
'designed' is an anagram indicator (designed with the letters).
'by' means one lot of letters go next to another.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'paris' with letters rearranged gives 'apris'.
'ho' going inside 'apris' is 'aphoris'.
'aphoris'+'m'='APHORISM'
(Other definitions for aphorism that I've seen before include "Maxim, short wise saying" , "A short, pithy, instructive saying" , "Brief pithy saying" , "One could briefly say this" , "Terse saying" .)