shorten vs diminish

shorten and diminish both are verbs.

Word	Noun	Adjective	Verb	Adverb
shorten	No	No	Yes	No
diminish	No	No	Yes	No

As verbs, diminish is a hypernym of shorten; that is, diminish is a word with a broader meaning than shorten:

Other hypernyms of shorten include decrease, fall, lessen.

shorten (verb)	diminish (verb)
become short or shorter	decrease in size, extent, or range
make shorter than originally intended; reduce or retrench in length or duration	lessen the authority, dignity, or reputation of
reduce in scope while retaining essential elements
edit by omitting or modifying parts considered indelicate
make short or shorter