Temperature in Rome high for rail system (5)
I believe the answer is:
metro
'rail system' is the definition.
'metro' can be an answer for 'system' (I have seen 'Underground system ' mean 'metro' so perhaps 'system' could also mean 'metro'). I am unsure of the 'rail' bit.
'temperature in rome high' is the wordplay.
'temperature' becomes 't' (abbreviation).
'in' means one lot of letters goes inside another.
'high' indicates an anagram (like drunk).
'rome' is an anagram of 'mero'.
't' placed into 'mero' is 'METRO'.
'for' is the link.
Can you help me to learn more?
(Other definitions for metro that I've seen before include "Parisian rail system" , "French underground" , "Paris subway" , "what moves many Parisians" , "The underground railway system in Paris" .)