Singular desire to be smart (5)
I believe the answer is:
swish
'be smart' is the definition.
(I've seen this before)
'singular desire' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'desire' becomes 'wish' (wish is a kind of desire).
's'+'wish'='SWISH'
'to' acts as a link.
(Other definitions for swish that I've seen before include "Impressively smart" , "Classy" , "Impressively fashionable" , "Smart; stylish" , "Sound of cane" .)