The word Abbreviate means reduce in scope while retaining essential elements. Thus, its antonym becomes to expand.
Antonyms of Abbreviate:
Antonyms of Abbreviate are to extend, lengthen, expand, amplify
Synonyms of Abbreviate:
To shorten, abridge, summarize, precis, cut down, trim, clip, abstract, digest, condense, compress, reduce, lessen, shrink and to contract etc