soap ball
A solid ball made of soap, often used for washing or as a craft item. Less common than the bubble sense.
I gave a handmade soap ball as a present.
soap bubble
A bubble made from soapy water; the more common meaning. Sometimes read しゃぼんだま, which is a variant reading influenced by シャボン玉.
See also: シャボン玉
The children were blowing soap bubbles in the park.
The soap bubble was shining beautifully.
Common mixed kanji-kana spelling; 石けん is a standard rendering of 石鹸.
Full kanji spelling; 石鹸 is the standard kanji for 'soap', but the compound is often written with kana for 石けん.
Compound of 石けん (soap) and 玉 (ball). The reading しゃぼんだま for the bubble sense is influenced by the more common synonym シャボン玉.