Largely put off about temperature in Nile region (5)

I believe the answer is:
delta
'nile region' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'largely put off about temperature in' is the wordplay.
'largely' means to remove the last letter (most but not all of the letters).
'put off' becomes 'delay' (I've seen this in another clue).
'about temperature' becomes 't' (abbreviation. I am not sure about the 'about' bit.).
'in' is an insertion indicator.
'delay' with its last letter taken off is 'dela'.
'dela' placed around 't' is 'DELTA'.
Can you help me to learn more?
(Other definitions for delta that I've seen before include "Greek letter in the shape of a triangle" , "Comms code for 'd'" , "Split river mouth system" , "Wing shape; Greek D" , "Alluvial river mouth" .)
