Alongside an animal bearing right (7)
I believe the answer is:
abreast
'alongside' is the definition.
(abreast means side by side or at the side of)
'an animal bearing right' is the wordplay.
'an' becomes 'a'.
'animal' becomes 'beast' (synonyms).
'bearing' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'beast' going around 'r' is 'breast'.
'a'+'breast'='ABREAST'
(Other definitions for abreast that I've seen before include "Familiar" , "Well-informed" , "Level in line" , "Level or keeping pace with" , "shoulder to shoulder" .)