In the morning, around ten after ten in truth (5)
I believe the answer is:
axiom
'truth' is the definition.
(thesaurus)
'in the morning around ten after ten' is the wordplay.
'in the morning' becomes 'am'.
'around' means one lot of letters goes inside another.
'ten' becomes 'io'.
'after' says to put letters next to each other.
'ten' becomes 'x' (roman numeral).
'io' put after 'x' is 'xio'.
'am' placed around 'xio' is 'AXIOM'.
'in' acts as a link.
(Other definitions for axiom that I've seen before include "Plainly true proposition" , "Clearly true statement" , "Established principle" , "Generally accepted proposition" , "Old saying or precept 95)" .)