by all odds vs decidedly

by all odds and decidedly both are adverbs.

Word	Noun	Adjective	Verb	Adverb
by all odds	No	No	No	Yes
decidedly	No	No	No	Yes

As adverbs, by all odds and decidedly are synonyms defined as:

Other synonyms of by all odds include definitely, emphatically, in spades, unquestionably.

by all odds (adverb)	decidedly (adverb)
without question and beyond doubt	without question and beyond doubt