noun
Used to state the reason or cause for something, often in formal or written contexts. Frequently appears in the pattern ～が故に or ～故の.
貧しさ故に、彼は進学を諦めた。
Because of poverty, he gave up on going to higher education.
経験不足故の失敗だった
conjunction
because of; as a result of
Conjunctive use, equivalent to ～のために or ～の理由で. Attaches to nouns or nominalized phrases, often in the form ～故（に）.
事故故に電車が遅れた。
The train was delayed because of an accident.
彼は若さ故に過ちを犯した。
He made a mistake because of his youth.
It was a failure due to lack of experience.
理由 is the common, everyday word for 'reason'. 故 is more formal and literary, often used in fixed expressions.
為 is the standard word for 'because of' or 'for the sake of'. 故 carries a more formal, sometimes archaic tone.
Derived from classical Japanese, where 故 (yue) meant 'reason' or 'cause'. The kanji 故 carries the meaning of 'reason' or 'circumstances'.