The affix ṭhak comes after a word in the Accusative -2nd case in construction when the sense is 'he gives', the motive being mean.,
Thus द्विगुणं प्रयच्छति = द्विगुणिकः 'a usurer who gives for the sake of double' i. e. who charges cent per cent interest. The word द्विगुण means द्विगुणार्थ 'for the sake of double'. Similarly त्रैगुणिकः ॥
Vart:- The word वृद्धि is changed to वृधुषि before this affix. As, वृद्धिं प्रयच्छति = वार्धुषिकः 'a usurer' 'who gives for the sake of increase' Or the word वृधुषि may be taken as a separate word synonymous with वृद्धि ॥
Why do we say गर्ह्यम् 'with a mean motive'? Observe द्विगुणं प्रयच्छति अधर्मणः 'the debtor gives double'.,