Synonyms for Broaden:

n.

burr, bur, cut glass, brogue, accented, broad, accent, drawl. incorporate, involve, count in, wide, include, add-on, take in, build in, embrace. smile, simper, raise a smile, grin/smile from ear to ear, smile thinly, beam, crack a smile, smirk, grin, force a smile/laugh. broaden (noun)
branch out, diversify.

v.

expand (verb)
stretch, spread, swell, engorge, dilate, distend, develop, thicken.
extend, supplement (verb)
expand, grow, develop, fatten, augment, stretch, increase, spread, enlarge, swell, widen.
increase (verb)
heighten, upgrade, grow, expand, raise, lengthen, maximize, increase, multiply, widen, boost, augment, magnify, accrue, add, inflate, reinforce, increment, burgeon, extend, enlarge, fatten, advance, amplify, elevate.
thicken (verb)
thicken, expand, widen.

Other synonyms:

cut glass, burr, drawl, brogue, accented, broad, accent, open out. collapse, flare. expand
thicken, expand, open out.
open up
widen.
Other relevant words:
broad, branch out, flare, drawl, open out, accented, collapse, burr, amplify, diversify.

Usage examples for broaden

  1. That Bible- I think I did grow and broaden after leaving school, but I never grew beyond Psalms and St. Paul; which proves that a little knowledge is not dangerous." – Dan Merrithew by Lawrence Perry
  2. I want to hear about this world, this world I am going to leave, and how you think you are going on fighting in the hot and dusty struggle- to make the world cool and kind and reasonable, to train minds better, to broaden ideas ... – The Passionate Friends by Herbert George Wells