Still covers like fungus (5)
I believe the answer is:
yeast
'fungus' is the definition.
(yeast is a kind of fungus)
'still covers like' is the wordplay.
'still' becomes 'yet' ('yet' can be a synonym of 'still').
'covers' indicates putting letters inside.
'like' becomes 'as'.
'yet' going around 'as' is 'YEAST'.
(Other definitions for yeast that I've seen before include "fermenter" , "Androgynous" , "Bread-making component" , "Leavening agent in bread-making" , "Agent for making bread" .)