Is samadhi the same as samatha? Is there khanika samatha?

I read the following on the internet: > Notice there's a wide spectrum on the Samatha/Vipassana scale, but > even on the extreme spectrum of Vipassana, the "dry-insight", there's > still element of Samatha ( the khanika/Samadhi/Momentary Concentration, > see Ven. Gunaratana's "The Jhanas" for more details ). It is said the Buddhist commentaries refer to Khanika (momentary), Upacara (neighborhood) and Appana (attainment) Samadhi. Are 'samatha' & 'samadhi' synonymous? Does Buddhism refer to Khanika/Momentary Samatha?