Transport system encounterd by Robert Oppenheimer initially (5)
I believe the answer is:
metro
'transport system' is the definition.
(I've seen this before)
'encounterd by robert oppenheimer initially' is the wordplay.
'encounterd' becomes 'met' (I am not sure about this - if you are sure you should believe this answer much more).
'by' says to put letters next to each other.
'initially' says to take the initial letters.
The initial letters of 'robert oppenheimer' is 'ro'.
'met'+'ro'='METRO'
Can you help me to learn more?
(Other definitions for metro that I've seen before include "French underground" , "Paris underground rail system" , "Parisian underground railway" , "Parisian rail system" , "what moves many Parisians" .)