verb
-ens; -ened; -ening
[+ obj] :to make (something) sharp or sharper
[+ obj] :to make (something) clearer or more distinct
[no obj] :to become clearer or more distinct
[+ obj] :to improve (something)
[no obj] :to become more severe
sharpen up
[phrasal verb]
to become better, smarter, more skillful, etc.