Expression of gratitude not so much found in Times - almost forbidden (5,3)
I believe the answer is:
bless you
'expression of gratitude' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.
'not so much found in times almost forbidden' is the wordplay.
'not so much' becomes 'less' (I've seen this before).
'found in' indicates putting letters inside.
'times' becomes 'by' (both can mean 'multiplied by').
'almost' means to remove the last letter (most of the word but not all of it).
'forbidden' becomes 'out' (synonyms).
'less' put within 'by' is 'blessy'.
'out' with its final letter taken away is 'ou'.
'blessy'+'ou'='BLESS YOU'
Can you help me to learn more?
(Other definitions for bless you that I've seen before include "It's said after a sneeze" , "Prayer" , "remark following ejection?" , "Gesundheit!" , "often follows sudden explosion!" .)