Meaning is defined by context not vice versa (This is my mantra, btw). The usage of tokos to denote "interest" or "usury" is a metaphorical usage of the word "tokos." I'm guessing that the interest is the "offspring" of the principal that was loaned and thus came to be seen metaphorically as "tokos." Here's the link to assure you that the primary meaning of the wordtokos simply is to give birth to. Notice the primary meaning of the word and then the secondary meaning that is given.
Where did he use it?
Is it used anywhere else in Scripture to mean "mother" or "bearer"
Is "tokos" ever translated in Scripture to mean "mother or bearer".
What word did Jesus use to refer to his mother: "tokos" or "meter".