noun, noun or participle which takes 'suru', intransitive verb
penile erection; becoming erect; stiffening
A direct physiological or medical term, most commonly for erection of the penis. As a suru verb it is intransitive: 陰茎が勃起する, not 陰茎を勃起する.
性的刺激を受けると、陰茎が勃起することがある。
The penis may become erect when sexually stimulated.
勃起が長く続く場合は、医師に相談してください。
If an erection lasts a long time, please consult a doctor.
noun, noun or participle which takes 'suru', intransitive verb
welling up of emotion; surge of feeling
Rare, literary, and potentially old-fashioned use for an emotion suddenly rising up. In modern ordinary Japanese, words such as わき起こる or 高まる are more natural.
古い文章では、「怒りが勃起する」のように、感情が急にわき起こる意味で使われることがある。
In older writing, 勃起する can be used in expressions like “anger wells up,” meaning that an emotion suddenly arises.