As an adverb extremely
is (degree) to an extreme degree.
As an adjective uttermost is
outermost.
As a noun uttermost is
the utmost; the highest or greatest degree; the farthest extent.
uttermost
English
Adjective
(
-)
Outermost
Extreme; utmost; being; in the farthest, greatest, or highest degree.
* (rfdate) Psalms 65:8
- They also that dwell in the uttermost parts are afraid at thy tokens: thou makest the outgoings of the morning and evening to rejoice.
Noun
The utmost; the highest or greatest degree; the farthest extent
(
Webster 1913)