Don't say anything - it's trendy to show part of leg (4)
I believe the answer is:
shin
'leg' is the definition.
(I have seen 'Lower leg ' mean 'shin' so perhaps 'leg' could also mean 'shin')
'don't say anything it's trendy to show part' is the wordplay.
'don't say anything' becomes 'h' (I can't explain this - if you can you should believe this answer much more).
'it's trendy' becomes 'in' ('in' can mean fashionable).
'to' means one lot of letters go next to another (I've seen this in other clues).
'part' suggests taking the first letters.
The first letter of 'show' is 's'.
'h'+'in'='hin'
'hin' put after 's' is 'SHIN'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for shin that I've seen before include "Cut of beef; part of leg" , "letter from Israel" , "Body part" , "kick" , "Lower foreleg" .)