dripping with sweat; soaked in sweat
Describes a person or body part that is visibly drenched in sweat, often from heat or exertion. Used as a な-adjective or noun.
He became drenched in sweat because of the heat.
He was dripping with sweat when he came back from jogging.
I changed out of my sweat-soaked shirt.
She was working while drenched in sweat.
The sweat-drenched athlete arrived at the goal.
びしょびしょ is a general onomatopoeia for being soaking wet from any liquid, while 汗だく specifically describes being drenched in sweat.
Compound of 汗 (あせ, 'sweat') and だく, a suffix meaning 'drenched' or 'soaked', likely related to the verb 抱く (だく, 'to hold') with a sense of being enveloped in sweat.