natthaññaṁ

accusative singular neuter of natthaññu (or instrumental form with suffix, alternate reading natthaññatāya); from na + attha + aññu, 'one who has no other purpose/benefit'; rare contracted form

for no other purpose
for no benefit
in vain

Built from

na — prefix · not, without
Plain negation. The prefix na- (without) negates the following compound.
attha — root · purpose, benefit
Derived from √arth- (to aim, purpose); Sanskrit artha. The word denotes material or purposeful advantage.
aññu — root · other, different
Sanskrit anya, meaning 'other' or 'different'; the form aññu is the nominative stem here functioning attributively.

Analysis. na + attha + aññu: 'not' + 'purpose, benefit' + 'other'; the phrase 'natthaññaṁ' (for no other purpose) appears in Pali suttas to denote an action performed without ulterior motive or practical gain.

Etymology. na- (negation prefix, English un-) + attha (purpose, benefit; Sanskrit artha, cognate with Latin artis, Greek arthron, via the sense of 'joint' as that which holds things together, hence 'purpose, aim') + aññu (other, different; from anya- 'other', cognate with Sanskrit anya, possibly related to the root of Latin alius). The locution idiomatically means 'without another purpose', emphasizing disinterested or purposeless action.

Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.

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