Fix one Frenchman somewhere to sleep (5)
I believe the answer is:
imbed
'fix' is the definition.
(thesaurus)
'one frenchman somewhere to sleep' is the wordplay.
'one' becomes 'I' (Roman numeral).
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'somewhere to sleep' becomes 'bed'.
'i'+'m'+'bed'='IMBED'
(Other definitions for imbed that I've seen before include "Firmly establish" , "Implant" , "Fix deeply into surroundings" , "Enclose deeply or snugly" , "Become deeply fixed" .)