Dear HopeSeeker,
As-salamu alaykum
The root 'K-TH-R', forms different many words in the Quran which are used numerous times such as 'Kathir' (many, abundantly, manifold, much), 'kathrah' (multitude, abundance), the verb: 'kaththara', 'akthara' (multiply, much) etc. There is a consistent meaning of the root and the words in the main that are formed form it.
Thus I incline to interpret it in a similar manner referring to something which denotes abundance.
I hope that helps, God willing
Joseph