His speech may seem endless! (6)
I believe the answer is:
orator
'his speech may seem endless' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
This is all the clue.
Can you help me to learn more?
(Other definitions for orator that I've seen before include "Eloquent type" , "A fluent public speaker" , "he can talk" , "Rhetorician" , "One who holds forth" .)