susceptible

Etymology

From Late Latin susceptibilis, from Latin susceptus, from suscipiō.

adj

1. likely to be affected by something
   He was susceptible to minor ailments.
2. easily influenced or tricked; credulous
3. (medicine) especially sensitive, particularly to a stimulus
4. that, when subjected to a specific operation, will yield a specific result
   Rational numbers are susceptible of description as quotients of two integers.
   A properly prepared surface is susceptible of an enduring paint job.
5. vulnerable
   The visitors were being pinned back by the end of the first half. Yet Gordon Strachan's side played with great conviction and always had a chance of springing a surprise when their opponents were so susceptible at the back. 14 August 2013, Daniel Taylor, The Guardian

noun

1. (epidemiology) A person who is vulnerable to being infected by a certain disease
   In either instance a decrease in the number of susceptibles, by making the spread of virus less easy, tends towards a stage at which the infection dies out. 1983, Topley & Wilson, editors, General Microbiology & Immunity, page 417