What do call embedded words? [closed]

A word embedded in the manner you mention (as, for example, star within stellar, or sun within sanguine) can be said to be a subsequence:

In mathematics, a subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements. For example, the sequence <A,B,D> is a subsequence of <A,B,C,D,E,F>.

Since a word is a sequence of letters, one might by analogy with subsequence speak of a subword, except that in wiktionary subword is defined as "(mathematics) substring", and substring implies contiguity of symbols, which subsequence does not.