It's smooth and shiny as tin, perhaps. (5)
I believe the answer is:
satin
'it's smooth' is the definition.
(similar in meaning)
'as tin perhaps' is the wordplay.
'perhaps' is an anagram indicator.
'as'+'tin'='astin'
'astin' is an anagram of 'SATIN'.
'and shiny' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for satin that I've seen before include "Stain on shiny cloth" , "Stain found in cloth" , "Smooth glossy fabric" , "Saint (anag.)" , "Glossy textile" .)