Completely surrounded by liquid, especially water; also means deeply absorbed or engaged in something.
From Latin immergere, from in- (in) + mergere (to dip or plunge). The word entered English in the 15th century. The figurative meaning developed by the 19th century.
Humans can hold their breath for about 2 minutes, but when immersed in cold water, the 'mammalian dive reflex' kicks in and some people have survived immersion for 45 minutes! This ancient reflex is a leftover from our aquatic ancestors.
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