Thaw encountered around heart of Himalayas (4)
I believe the answer is:
melt
'thaw' is the definition.
(synonyms)
'encountered around heart of himalayas' is the wordplay.
'encountered' becomes 'met' ('meet' can be a synonym of 'encounter').
'around' means one lot of letters goes inside another.
'heart of' means to look at the middle letters.
The central letter of 'himalayas' is 'l'.
'met' enclosing 'l' is 'MELT'.
(Other definitions for melt that I've seen before include "become soft" , "Dissolve with heat" , "Liquefy; become tender" , "Become liquid by heating" , "Thaw" .)