Stretchy fabric (5)
'stretchy fabric' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lycra that I've seen before include "skin-tight garments" , "Elasticated synthetic material" , "Stretchy fabric" , "Sports clothing material" , "gear for cyclists" .)
(Other definitions for elastic that I've seen before include "Flexible rubber strip" , "Flexible (material)" , "'Flexible, springy (7)'" , "Something stretchy" , "Pliable" .)