Wild bears in a forest at last, side by side (7)
I believe the answer is:
abreast
'side by side' is the definition.
('abreast' can be a synonym of 'side by side')
'wild bears in a forest at last' is the wordplay.
'wild' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'at last' says to take the final letters.
The last letter of 'forest' is 't'.
'bears' is an anagram of 'breas'.
'a'+'t'='at'
'breas' put into 'at' is 'ABREAST'.
(Other definitions for abreast that I've seen before include "Alongside one another and facing the same way" , "shoulder to shoulder" , "Familiar" , "Side by side; keeping pace" , "Level or keeping pace with" .)