Ablative. What is the meaning of atthā?

Attha1: 6. adverb. use of oblique cases in the sense of a preposition.:

(a) dative. atthāya: for the sake of, in order to, for J i.254 dhanɔ atthāya for wealth, kim° what
for, why?), 279; ii.133; iii.54; DhA ii.82; PvA 55, 75, 78. —

(b) accusative. atthaṁ: on account of, in order to, often instead of an infinitive or with another infinitive. substitute J i.279

© ablative. atthā J iii.518 (pitu atthā = atthāya C.). —

(d) loc. atthe: instead of, for