I described 'Piglet' as 'Pit' containing 'leg, originally' (5)
I believe the answer is:
milne
'i described piglet' is the definition.
The definition suggests a singular noun which matches the answer.
'pit containing leg originally' is the wordplay.
'pit' becomes 'mine' (I've seen this before).
'containing' is an insertion indicator.
'originally' suggests taking the first letters.
The initial letter of 'leg' is 'l'.
'mine' placed around 'l' is 'MILNE'.
'as' is the link.
Can you help me to learn more?
(Other definitions for milne that I've seen before include "Winnie-the-Pooh author" , "Children's author" , "Creator of Eeyore" , "Writer of Winnie the Pooh" , "He wrote stories for his son, Christopher Robin" .)