Where does “giddysome” come from?

giddysome (English) comes from English -some, from Middle English -som, from Old English sum, from Proto-West Germanic *sum, from Proto-Germanic sumaz, from Proto-Indo-European sem- — together, one.

Ancestry of “giddysome”, step by step

Step	Language	Word	Meaning
1	English	-some	Characterized by some specific condition or...
2	Middle English	-som	some; having a specific quality
3	Old English	sum	some
4	Proto-West Germanic	*sum	some
5	Proto-Germanic	sumaz	some (one), a certain (one)
6	Proto-Indo-European	sem-	together, one

Every word from Proto-Indo-European sem- →Every word from Proto-Germanic sumaz →Every word from Proto-West Germanic *sum →