Sentence:  It is often convenient to view a <WSD>monic</WSD> arrow i: A \rightarrowtail C, defined in Chapter 1, as showing that "A" is a copy of a part of "C", and that "i" maps the copy on to that part. For example, in Set, the <WSD>monic</WSD> arrows are the one-to-one functions and, clearly, if "i" is one-to-one then "A" is a copy of a subset of "C", namely of the image of "i". 
Meaning of the word marked with <WSD> tags:  "Of a morphism": that it is a monomorphism.