Comedian periodically nearly faltering (7)
I believe the answer is:
doddery
'faltering' is the definition.
(I've seen this before)
'comedian periodically nearly' is the wordplay.
'comedian' becomes 'dodd' (Ken Dodd).
'periodically' indicates alternate letters (letters must be selected 'every so often').
The alternate letters of 'nearly' are 'ery'.
'dodd'+'ery'='DODDERY'
(Other definitions for doddery that I've seen before include "Shaky" , "Old and infirm" , "Rather senile" , "Old and feeble" , "Infirm with age" .)