Mamoi Tamul is a variety of palm nut. It's binomial name is Chrysalidocarpus lutescens. Chrysalidocarpus lutescens is a cousin of the larger areca palm (Tamul), that produces betel nuts which can be chewed with betel leaf. (Check 'Areca palm and betel leaf')
The size of the mamoi tamul is smaller than the betel nut. The husk of the mamoi tamul seeds become yellow when matured and the fruit inside becomes hard. Mamoi tamul can also be chewed like betel nut with or without betal leaf.