Bit of grass scouts lost on summit of Kilimanjaro (7)
I believe the answer is:
Here is my best explanation:
'bit of grass' is the definition.
'scouts lost on summit of kilimanjaro' is the subsidiary indication.
'lost' indicates anagramming the letters.
'on' is a charade indicator (letters next to each other).
'summit of' suggests taking the first letters.
The first letter of 'kilimanjaro' is 'k'.
'scouts' anagrammed gives 'tussoc'.
(Other definitions for tussock that I've seen before include "Grass clump", "Grassy clump", "Clump of hair", "Dense clump of grass - stuck so (anag)", "Thick patch of grass", "hump", "(Of grass) cut", "Clump of grass", "Tuft of grass" and "Bushy clump of grass".)