there is an excellent resource at blueletterbible.org
bring up a verse, Gen 1:5 for example
then click on the left handed box labelled C
it will bring up a lexicon and concordance.
for example:
the word in Hebrew translated as called is qara.
it is a consistent naming process through Gen 1-2
in this verse God calls the period of light--> yom,
this is explicitly opposed to the definition of night as the time period where darkness reigns.
no where else does this structure of "A qara B" occur with B=yom.
but i'd be interested if anyone else has seen where God calls yom anything else. yom is used in lots of ways, but AFAIK this is the only place it is defined.