What is the X in X-mas?
1560s, from Latin segmentum "a strip or piece cut off, a cutting, strips of colored cloth," from secare "to cut" (see section (n.)), with euphonious alteration of -c- to -g- before -m-. Latin segmentum was used in Medieval Latin as a geometry term, translating Greek tmema, and the word was first picked up in English in this sense. Meaning "segmental portion of anything circular" is from 1640s; general sense of "a division, section" is from 1762.
1859, intransitive, in reference to cell division, from segment (n.). Transitive sense, "divide (something) into segments" is from 1872. Related: Segmented; segmenting.
segment seg·ment (sěg'mənt)
A clearly differentiated subdivision of an organism or part, such as a metamere.
A part of an organ having independent function, supply, or drainage.