This is an outdated term for oral sex. It does not imply any particular gender or power orientation. This is very common in Victorian era erotic writing.
trans. To practise fellatio or cunnilingus (with); also intr. Also as n. Hence gamahucher.
The Count and I often sandwiched them between us, which they declared
to be the _ne plus ultra_ of pleasure, while the upper operator
gamahuched the unoccupied quim.