khamak (percussion string instrument)

This instrument is known by Very Many names, it has many sub-types and confusable similar instruments;
The names are usually onomatopoeic such as "gubaguba" or variations on "khamak", the term "anandalahari" seems to be literary in nature

The khamak type is shaped like a barrel, it has a pin, bit of wood or even a clay pot at the opposite end of the string
The bhapang type is shaped like a goblet drum, its string attached on the *outside* of the membrane
The katho type has the string and membrane like the same as bhapang, but is shaped like a barrel, again

see https://atlasofpluckedinstruments.com/india.htm for images of tokari and gopichand and compare with the illustration of khamak. (note that grove music online is absolutely incorrect about this instrument, it is presented as a variable tension chordophone, but it is indeed closer to a lute, similar to the dotara)

About ektar/ektara confusion:
Several different instruments are called "extar/iktar/yaktaro" etcetera. it causes confusion not only with these instruments, but *also* wider when similar instruments to (one) of the ektar types is written as "similar to the ektara" and this is then taken to be similar to another type of ektar, further still when two such "similar to ektar" instruments are then considered similar to *each other* while actually having only the "one string" in common.
This is why the tokari (which is similar to the lute dotara) is said to be similar to the variable tensioned stringed drum khamak/gubguba, because those are said to be similar to the one spoke tuntuna, which has an alias of "ektar" because it is compared with the gopychant two pronged instrument, while the thumbi, a bengali one stringed lute *also* is named "ektar" (probably where the confusion of tokari = ektar came from) (eg https://indianculture.gov.in/musical-instruments/tat-vadya/tokari )

When researching instruments make sure you have the right type of instrument! Often images will be a great help!