1. 潜心钻研;专心
Someone's immersion in a subject is their complete involvement in it.

e.g. ...long-term assignments that allowed them total immersion in their subjects.
可以让他们潜心研究课题的长期任务

2. 浸没;浸泡
Immersion of something in a liquid means putting it into the liquid so that it is completely covered.

e.g. The wood had become swollen from prolonged immersion.
因长时间浸泡，木头发胀了。

noun

1. the act of wetting something by submerging it

Synonym: submersionduckingdousing

2. a form of baptism in which part or all of a person's body is submerged

3. complete attention
intense mental effort

Synonym: concentrationengrossmentabsorption

4. (astronomy) the disappearance of a celestial body prior to an eclipse

Synonym: ingress

5. sinking until covered completely with water

Synonym: submergencesubmergingsubmersion