Smaller, being younger (5)
I believe the answer is:
minor
I believe this is a triple definition!
'smaller' is the first definition.
(I've seen this before)
'being' is the second definition.
(minor is a kind of being)
'younger' is the third definition.
(thesaurus)
(Other definitions for minor that I've seen before include "Unimportant or unable to vote" , "Morris car; tending to melancholy (mus.)" , "Of lesser importance" , "Slight; little known" , "One hasn't reached legal majority" .)