The affix ṭhak comes in the sense of 'who dwells' after the Locative word nikaṭa,
This rule applies in forming epithets, denoting such persons, who are allowed under the Sacred Institutes, to dwell near human habitations. Thus आरण्यकाः are those ascetics who are ordained to dwell in forests, at least two miles away from human habitations. नैकटिकाः are those ascetics who are allowed by the rule of their Order to live near human habitations. Thus निकटे वसति = नैकटिकः 'an ascetic.',