I react excitedly, having screened old smut (7)
I believe the answer is:
erotica
'old smut' is the definition.
The definition suggests a singular noun which matches the answer.
'i react excitedly having screened' is the wordplay.
'excitedly' is an anagram indicator.
'having' means one lot of letters goes inside another.
'screened' becomes 'o' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i'+'react'='ireact'
'ireact' with letters rearranged gives 'ertica'.
'ertica' enclosing 'o' is 'EROTICA'.
Can you help me to learn more?
(Other definitions for erotica that I've seen before include "Writing of a sexual nature" , "(Items of) titillating art" , "Sexually explicit art" , "Salacious" , "Porn" .)