WordNet sense 1 (extend in one or more directions):

spread out

WordNet sense 2 (add details, as to an account or idea; clarify the meaning of and discourse in a learned way, usually in writing):

dilate, elaborate, enlarge, expatiate, expound, lucubrate, exposit, elaborate, flesh out

WordNet sense 3 (expand the influence of):

extend

WordNet sense 4 (grow stronger):

boom, flourish, prosper, thrive, get ahead

WordNet sense 5 (exaggerate or make bigger):

amplify, inflate, blow up