Basic, poorly spelt article intrudes (6)
I believe the answer is:
staple
'basic' is the definition.
(synonyms)
'poorly spelt article intrudes' is the wordplay.
I cannot really see how this works, but
'article' could be 'a' (the indefinite article in English) and 'a' is present in the answer.
an anagram of 'spelt' is 'stple' which is located in the left over letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for staple that I've seen before include "A wire paper fastener for plates" , "U-shaped wire to fasten papers together" , "Paper fastening" , "key" , "Important; paper fastener" .)