Speak at length at entering to make amends (9)
I believe the answer is:
expatiate
'speak at length' is the definition.
'expatiate' can be an answer for 'speak' (thesaurus). I am unsure of the 'at length' bit.
'at entering to make amends' is the wordplay.
'entering' means one lot of letters goes inside another.
'to make amends' becomes 'expiate' (I've seen this in another clue).
'at' put within 'expiate' is 'EXPATIATE'.
Can you help me to learn more?
(Other definitions for expatiate that I've seen before include "Speak/write in detail (on)" , "Go into detail" , "write in great detail" , "In detail, discuss" , "Speak in detail (on)" .)