It should include these mountains (5)
I believe the answer is:
atlas
'these mountains' is the definition.
(I've seen this before)
'it should include' is the wordplay.
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'should' becomes 'alas' (I can't justify this - if you can you should believe this answer much more).
'include' indicates putting letters inside.
't' put within 'alas' is 'ATLAS'.
Can you help me to learn more?
(Other definitions for atlas that I've seen before include "A geog. book; N. African range" , "book of world records?" , "Supporter of the classics" , "Its architectural name is telamon" , "Giant" .)