In nonstandard|lang=en terms the difference between supposably and supposingly
is that supposably is (nonstandard) supposedly while supposingly is (nonstandard) supposedly.
As adverbs the difference between supposably and supposingly
is that supposably is able to be supposed or conjectured while supposingly is (nonstandard) supposedly.
supposably
English
Adverb
(-)
Able to be supposed or conjectured.
(nonstandard) Supposedly.
Synonyms
* (able to be supposed) conceivably, imaginably
* (supposedly) purportedly
supposingly
English
Adverb
(-)
(nonstandard) supposedly