Number with a name that's well known (5)
I believe the answer is:
noted
'well known' is the definition.
(I've seen this in another clue)
'number with a name' is the wordplay.
'number' becomes 'no' (abbreviation for 'number').
'with' means one lot of letters go next to another.
'a name' becomes 'ted' ().
'no'+'ted'='NOTED'
'that's' acts as a link.
(Other definitions for noted that I've seen before include "written down" , "Observed - recorded" , "Remarked - famous" , "Like music" , "Distinguished" .)