Without doubt involved in chance RTA in Lyons (9)
I believe the answer is:
certainly
'without doubt' is the definition.
(thesaurus)
'involved in chance rta in lyons' is the wordplay.
'involved in' says the answer is hidden in the clue.
'CERTAINLY' can be found hidden inside 'chance rta in lyons'.
(Other definitions for certainly that I've seen before include "Of course" , "Undoubtedly" , "Definitely, surely" , "Assuredly" , "Without doubt" .)