Indeterminably is defined as not being able to be determined or decided. There are several synonyms for the word indeterminably, including indefinitely, immeasurably, interminably, perpetually and eternally. These adverbs indicate a lack of finality or limit. Indefinitely suggests an unbounded time period, while immeasurably implies that something cannot be accurately measured or defined. Interminably means without an end, and perpetually suggests something enduring or unchanging, often in a negative way. Eternally refers to something happening throughout time without beginning or end. All these synonyms convey the idea of something that is impossible to determine, limit, or end.