Widen, v. t. [imp. & p. p. Widened; p. pr. & vb. n. Widening.]
To make wide or wider; to extend in breadth; to increase the width of; as, to widen a field; to widen a breach; to widen a stocking.
1 other Webster entry under this spelling
Widen, v. i.
To grow wide or wider; to enlarge; to spread; to extend. Arches widen, and long aisles extend. Pope.
Shades of meaning
Fernald has no entry of its own for widen; he lists it under amplify.
Where he writes about it:
We may develop a thought, expand an illustration, extend a discussion, expatiate on a hobby, dilate on something joyous or sad, enlarge a volume, unfold a scheme, widen the range of treatment. — from amplify