Like the Circle Line, it's part of the Underground (5)
I believe the answer is:
round
'like' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'the circle line it's part of the underground' is the wordplay.
'ROUND' is hidden in amongst the letters.
However, I am not sure how this is indicated.
Can you help me to learn more?
(Other definitions for round that I've seen before include "stage of competition" , "regular series" , "Regular route for a sentry" , "Drinks order" , "Division of a boxing match - having a curved shape - drinks bought by one person" .)