Possible effect of giving us port! (6)
I believe the answer is:
stupor
'possible effect' is the definition.
The definition and answer can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'of giving us port' is the wordplay.
'of' is an anagram indicator (the answer comes from or 'of' the letters).
'giving' means one lot of letters go next to another.
'us' put next to 'port' is 'usport'.
'usport' is an anagram of 'STUPOR'.
Can you help me to learn more?
(Other definitions for stupor that I've seen before include "State of insensibility or near-unconsciousness" , "numbness" , "State of dazedness or bemusement" , "State of bewilderment" , "Daze, semi-consciousness" .)