Anchored conifer on mountain top (4)
I believe the answer is:
firm
'anchored' is the definition.
(thesaurus)
'conifer on mountain top' is the wordplay.
'conifer' becomes 'fir' (fir is a kind of conifer).
'on' means one lot of letters go next to another.
'top' suggests taking the first letters.
The initial letter of 'mountain' is 'm'.
'fir'+'m'='FIRM'
(Other definitions for firm that I've seen before include "Not soft or yielding to pressure" , "Steady commercial organisation?" , "Company - solid" , "Business company" , "corporation?" .)