A small point that's relevant (3)
I believe the answer is:
apt
'relevant' is the definition.
(I've seen this before)
'a small point' is the wordplay.
'small point' becomes 'pt' (**).
'a'+'pt'='APT'
'that's' acts as a link.
(Other definitions for apt that I've seen before include "Tap (anag.)" , "Ready to learn" , "Train" , "Pertinent" , "Apposite, appropriate" .)