Oddly silky and insidious (3)
I believe the answer is:
sly
'insidious' is the definition.
(thesaurus)
'oddly silky' is the wordplay.
'oddly' indicates alternate letters.
The alternate letters of 'silky' are 'SLY'.
'and' is the link.
(Other definitions for sly that I've seen before include "'Cunning, wily (3)'" , "Cunning; surreptitious" , "'Crafty, cunning (3)'" , "Devious and furtive" , "Sneaky" .)