Paronomasia
Paronomasia , noun
[Latin, from Greek {not transcribed}, from {not transcribed} to form a word by a slight change; para` beside + {not transcribed} to name, from 'o`noma a name.]
(Rhetoric) A play upon words; a figure by which the same word is used in different senses, or words similar in sound are set in opposition to each other, so as to give antithetical force to the sentence; punning. — Dryden