1. encroach a relationship held together by a thread; easily broken 2. perennial to intrude upon or break through barriers set up by others 3. physiology the study of the physical body and how it works 4. tenuous something that continues nonstop for an indefinite period of time

Explanation:

The above words have been combined, each one, with its real meaning. For this, it was considered the conceptualization of each meaning related to the construction of the phrases shown and the meaning that each of them expresses. Dictionaries were also used to make sure which sentence had the meaning of the word and allowing the sentence to make sense.

answer; proximity;

the branch of biology that deals with the normal functions of living organisms and their parts.

the way in which a living organism or bodily part functions.