Final answer:
The suffix that signifies tightening or stricture, especially in anatomical terms, is '-spasm' as seen in the context of an anatomical sphincter.
Step-by-step explanation:
Identify the suffix from its meaning: Tightening; stricture: In the field of biology, particularly when discussing anatomy, the terms often consist of roots, prefixes, and suffixes. When we talk about tightening or stricture, we are referring to a constriction or tightening of a passage or vessel within the body. There are various suffixes used in medical terminology to describe such conditions, but one that is particularly associated with the tightening or contraction of muscles is -spasm. An anatomical sphincter for example, which is a circular muscle that can tighten to close off the flow through a passage or opening in the body, can go into spasm, thus 'tightening' and creating stricture.