Why no 'b' in numeric etc

"Number" vs. "Numeric"

Also "Enumerate" etc.

If I were to guess, I might go for it relating to "Numeral", but I don't see why it should derive from the less common word, nor why Numeral has no b itself.

In fact the odd-one-out is the word number. The words enumerate and numeral come more directly from Latin whereas 'number' comes to us via French and only indirectly from Latin.

In cases like this I recommend an etymology dictionary such as Online Etymology Dictionary.

origin of number "from Anglo-French noumbre, Old French nombre"

origin of numeral "from Middle French numéral (late 15c.), from Late Latin numeralis "of or belonging to a number," from Latin numerus "a number"

EDIT

I suppose you could now ask why there were two spellings in French! I guess that is a question for a French etymology dictionary and so not really on-topic here. Let's see if anyone else can answer that part. Alternatively you could ask on the French site. They accept questions written in English and one of the members might have just the right dictionary.