It makes me talk endlessly - usually a hard thing (5)
I believe the answer is:
metal
'hard thing' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'it makes me talk endlessly usually a' is the wordplay.
I cannot quite see how this works, but
'it' could be 't' (abbreviation. e.g. in 'tis) and 't' is found within the answer.
'me' is present in the answer.
'a' is within the answer.
A single letter 'l' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for metal that I've seen before include "Silver or gold, say" , "Element such as iron, copper, zinc etc" , "Like steel cutlery" , "Copper, perhaps" , "Eg, iron, lead" .)