Insistent means "unwilling to let go or back down." If a salesperson is insistent, you may find it hard to walk away without buying something.
Insistent shares a root with the verb insist: the Latin word insistere, which means "persist, dwell upon, stand upon." If you are insistent, you won't take "no" for an answer, dwelling on your ideas, standing up for your position. Insistent can also mean "demanding attention," like the insistent ringing of the telephone at a busy office or the insistent cries of a hungry baby.
