Group from Everest losing heart after month (5)
I believe the answer is:
octet
'group' is the definition.
(octet is a kind of group)
'everest losing heart after month' is the wordplay.
'losing heart' says to hollow out the word (remove centre letters).
'after' means one lot of letters go next to another.
'month' becomes 'oct' (Oct is an example).
'everest' with its middle taken out is 'et'.
'et' put after 'oct' is 'OCTET'.
'from' is the link.
(Other definitions for octet that I've seen before include "Music for eight" , "A group of eight, may be singers" , "What takes members up to eighth" , "A group of eight instruments or voices" , "Eightsome" .)