A lexeme is an abstract way of referring to a set of words which are closely related through a shared root word. The words a lexeme consists of typically differ only in grammatical function, like inflectional categories including and not limited to number, tense, and gender, to form a paradigm.
It is often the case that a lexeme consists of many words, however there are some instances where a lexeme consists of only a single word.
In Skwxwu7mesh, /si7l/ is the single word in the lexeme that represents grandparents, grandmother, grandfather, grandaunt, and granduncle. There is no explicit gender distinction for these terms and therefore there is no need for multiple words in the lexeme. (Shipley, 1995, p. 94, 96)
Shipley, D. L. (1995). A structural semantic analysis of kinship terms in the Squamish Language. ICSNL, 30, 92-100.
Urbanczyk, S. (2011). Evidence from Halkomelem for word-based morphology. ICSNL, 46, 470-489.