Friend crossing border at an early stage (6)
I believe the answer is:
primal
'at an early stage' is the definition.
I can't tell whether this definition defines the answer.
'friend crossing border' is the wordplay.
'friend' becomes 'pal' (pal can mean a friend).
'crossing' indicates putting letters inside.
'border' becomes 'rim' (both can mean an edge).
'pal' enclosing 'rim' is 'PRIMAL'.
Can you help me to learn more?
(Other definitions for primal that I've seen before include "Original; chief" , "Original - basic" , "Relating to an early stage of evolution" , "Of an early stage of development" , "Most important (scream therapy?)" .)