Dear Nitin

Nucleophilicity (In the context of organic chemistry): Ability of a group with a lone pair of electrons to push another such group out of a carbon centre.

Basicity: Ability of a group to combine with a proton (Bronsted).
                Ability of a group to donate a lone pair (Lewis).

If you want detail information about the above topic

Please go through the below link:

https://www.quora.com/Organic-Chemistry-What-are-the-differences-between-nucleophilicity-and-basicity-1

All the best.