Small and lean? Grow taller on this (5)
I believe the answer is:
stilt
'grow taller on this' is the definition.
The definition suggests a singular noun which matches the answer.
'small and lean?' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'and' is a charade indicator (letters next to each other).
'lean?' becomes 'tilt' ('tilt' can be a synonym of 'lean').
's'+'tilt'='STILT'
Can you help me to learn more?
(Other definitions for stilt that I've seen before include "Walking pole; wader" , "Stout pole with a foot rest -- wading bird" , "gets one member off the ground" , "Wading bird; post" , "Supporting column driven into the ground - wading bird" .)