pledge vs plight

pledge and plight both are nouns.

Word	Noun	Adjective	Verb	Adverb
pledge	Yes	No	Yes	No
plight	Yes	No	Yes	No

As nouns, plight is a hyponym of pledge; that is, plight is a word with a more specific, narrower meaning than pledge:

Other hyponyms of pledge include guarantee, warrant, warrantee, warranty, guarantee, troth, vow.

As verbs, pledge and plight are synonyms defined as:

pledge (noun)	plight (noun)
a binding commitment to do or give or refrain from something	a solemn pledge of fidelity
a drink in honor of or to the health of a person or event	a situation from which extrication is difficult especially an unpleasant or trying one
someone accepted for membership but not yet fully admitted to the group
a deposit of personal property as security for a debt

pledge (verb)	plight (verb)
promise solemnly and formally	promise solemnly and formally
bind or secure by a pledge	give to in marriage
give as a guarantee
propose a toast to
pay (an amount of money) as a contribution to a charity or service, especially at regular intervals