retain vs prolong

retain and prolong both are verbs.

Word	Noun	Adjective	Verb	Adverb
retain	No	No	Yes	No
prolong	No	No	Yes	No

As verbs, prolong is a hypernym of retain; that is, prolong is a word with a broader meaning than retain:

retain: allow to remain in a place or position or maintain a property or feature
prolong: lengthen or extend in duration or space

Other hypernyms of retain include keep up, sustain.

retain (verb)	prolong (verb)
keep in one's mind	lengthen in time; cause to be or last longer
secure and keep for possible future use or application	lengthen or extend in duration or space
allow to remain in a place or position or maintain a property or feature
hold back within