I am frail wobbly but well-known (8)
I believe the answer is:
familiar
'well-known' is the definition.
(similar in meaning)
'i am frail wobbly' is the wordplay.
'wobbly' indicates an anagram.
'i'+'am'+'frail'='iamfrail'
'iamfrail' with letters rearranged gives 'FAMILIAR'.
'but' acts as a link.
(Other definitions for familiar that I've seen before include "spirit" , "Well known or easily recognised" , "Conversant with the witch's cat?" , "Well known or recognisable" , "Well-known, easily recognisable" .)