I am given stuff that is unimportant (10)
I believe the answer is:
immaterial
'unimportant' is the definition.
(I've seen this before)
'i am given stuff' is the wordplay.
'i am' becomes 'I'm' (contraction).
'given' means one lot of letters go next to another.
'stuff' becomes 'material' (synonyms).
'im'+'material'='IMMATERIAL'
'that is' acts as a link.
(Other definitions for immaterial that I've seen before include "unimportant" , "Irrelevant" , "of no importance" .)