title: Need to FillNa with a value from a different column on the same index
body: <p>My last line is the issue. What I'm trying to do is <code>fillna</code> in 'New Hire' with the 'New Hire' value on the same index as 'Trainer' and the 'Trainer' value needs to be included in one of the strings in <code>Words</code>.</p>
  <p>df:</p>
  <pre><code>   Trainer New_Hire
  0  Trainer1    Hire1
  1  Trainer2    Hire2
  2  Trainer3    Hire3
  3  Trainer4      NaN
  </code></pre>
  <p>desired df:</p>
  <pre><code>    Trainer New_Hire
  0  Trainer1    Hire1
  2  Trainer3    Hire3
  3  Trainer4    Hire2
  </code></pre>
  <p>Current Code:</p>
  <pre><code>import pandas as pd
  
  df = pd.DataFrame({'Trainer': ['Trainer1','Trainer2','Trainer3','Trainer4'], 
  'New_Hire':['Hire1','Hire2','Hire3', 0]})
  
  words = ['Hi, Trainer2', 'Hello Bob!', 'Bonjour, Fransico']
  
  for trainer in df['Trainer']:
      for word in words:
          if trainer in word:
              df['New_Hire'].fillna(?))
  </code></pre>