A brief point is relevant (3)
I believe the answer is:
apt
'relevant' is the definition.
(I've seen this before)
'a brief point' is the wordplay.
'brief point' becomes 'pt' (abbreviation for point; 'brief' indicates a short form).
'a'+'pt'='APT'
'is' acts as a link.
(Other definitions for apt that I've seen before include "Proper" , "Tending" , "Pertinent" , "Prone" , "Appropriate for Pat" .)