pension plan vs IRA

pension plan and IRA both are nouns.

Word	Noun	Adjective	Verb	Adverb
pension plan	Yes	No	No	No
IRA	Yes	No	No	No

As nouns, IRA is a hyponym of pension plan; that is, IRA is a word with a more specific, narrower meaning than pension plan:

pension plan: a plan for setting aside money to be spent after retirement
IRA: a retirement plan that allows you to contribute a limited yearly sum toward your retirement; taxes on the interest earned in the account are deferred

Other hyponyms of pension plan include 401-k, 401-k plan, individual retirement account, Keogh plan.

pension plan (noun)	IRA (noun)
a plan for setting aside money to be spent after retirement	a retirement plan that allows you to contribute a limited yearly sum toward your retirement; taxes on the interest earned in the account are deferred
	a militant organization of Irish nationalists who used terrorism and guerilla warfare in an effort to drive British forces from Northern Ireland and achieve a united independent Ireland