Hyponym‏ [Noun.]

‘When the meaning of the one form is included in the meaning of the another, the relationship is described as hyponymy. […] The concept of “inclusion” involved in this relationship is the idea that if an object is a rose, then it is necessarily a flower, so the meaning of flower is included in the meaning of rose. Or, rose is a hyponym of flower.
[…] We can also say that two or more words that share the same superordinate term are co-hyponyms.’

– Yule, G. 1985. The Study of Language Cambridge, United Kingdom: Cambridge University Press (2010) p. 118-119