indeclinable adverb (accusative neuter singular of sādhuka used adverbially)
Analysis. sādhu + -ka (diminutive/emphatic suffix) + -ṁ (accusative neuter marking). The core adverb sādhu means "well" or "rightly"; the suffix -ka intensifies or renders it more colloquial.
Etymology. From √sidh (accomplish, succeed), cognate with Sanskrit siddha "accomplished, successful", Latin sedēre "sit" (one who sits firm has succeeded), and English "steady". The root's sense of "accomplishment" evolved to "rightness" and "propriety".
Meanings from the Digital Pāḷi Dictionary; morphology and etymology by Claude.
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