As nouns the difference between proponent and ultraintuitionist

is that proponent is one who supports something; an advocate while ultraintuitionist is (rare) a proponent of ultraintuitionism; an ultrafinitist.

As an adjective proponent

is making proposals; proposing.

Ultrafinitism is a synonym of ultraintuitionism.

As nouns the difference between ultraintuitionism and ultrafinitism

is that ultraintuitionism is ultrafinitism while ultrafinitism is a form of finitism that is even more extreme in that it denies those constructs whose construction cannot be physically performed (such as a number that no human could have time to calculate).

As a noun echo

is echo (a reflected sound that is heard again by its initial observer).

As an adjective unechoing is

that does not echo; echoless.

Selacian is an alternative form of selachian.

As adjectives the difference between selacian and selachian

is that selacian is while selachian is (zoology) pertaining the superorder selachimorpha, division , or similar grouping, including extant sharks, or its members.

As nouns the difference between selacian and selachian

is that selacian is while selachian is (zoology) any organism of the superorder selachimorpha, any extant shark.

As a proper noun selachimorpha

is .

As an adjective selachian is

(zoology) pertaining the superorder selachimorpha, division , or similar grouping, including extant sharks, or its members.

As a noun selachian is

(zoology) any organism of the superorder selachimorpha, any extant shark.

As nouns the difference between sharks and selachian

is that sharks is while selachian is (zoology) any organism of the superorder selachimorpha, any extant shark.

As an adjective selachian is

(zoology) pertaining the superorder selachimorpha, division , or similar grouping, including extant sharks, or its members.

As nouns the difference between proponent and ultrafinitist

is that proponent is one who supports something; an advocate while ultrafinitist is a proponent of ultrafinitism.

As an adjective proponent

is making proposals; proposing.

As nouns the difference between ultrafinitism and ultrafinitist

is that ultrafinitism is (mathematics) a form of finitism that is even more extreme in that it denies those constructs whose construction cannot be physically performed (such as a number that no human could have time to calculate) while ultrafinitist is a proponent of ultrafinitism.

As nouns the difference between extreme and ultrafinitism

is that extreme is while ultrafinitism is (mathematics) a form of finitism that is even more extreme in that it denies those constructs whose construction cannot be physically performed (such as a number that no human could have time to calculate).

As nouns the difference between construct and ultrafinitism

is that construct is something constructed from parts while ultrafinitism is (mathematics) a form of finitism that is even more extreme in that it denies those constructs whose construction cannot be physically performed (such as a number that no human could have time to calculate).

As a verb construct

is to build or form (something) by assembling parts.