Got it! The answer is
DATUM / DATA.
The title refers to the fact that
the singular and plural forms of this word (changing the number) don't reflect standard English grammar, which may be confusing to some.
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Data Science Stack Exchange, currently still in beta and not a fully-fledged graduate site.
Plural at a pyramid bottom
Our four letters may lead to wisdom
DATA (the 4-letter plural form) is at the bottom of the DIKW pyramid, also known as the Wisdom Hierarchy:
Singular with five to locate from
In New Zealand a peak is my home.
DATUM (the 5-letter singular form) can be found in geodesic datum, a system for locating points on the Earth, and also Datum Peak in New Zealand.
It's a nice riddle, and the clues all fit together in a clear and obvious way once you find the answer (all the best riddles have self-justifying solutions). However, the solution is quite difficult to come up with, and the clues don't all feel completely 'natural' (e.g. did you really know about that peak in New Zealand before you came across it as a way of cluing in the singular form?)