1. From Oxford Dictionaries (http://www.oxforddictionaries.com/us/definition/american_english/spinster):  
derogatory: An unmarried woman, typically an older woman beyond the usual age for marriage.
2. From Merriam-Webster (http://www.merriam-webster.com/dictionary/spinster): 
Simple Definition of spinster: an unmarried woman who is past the usual age for marrying and is considered unlikely to marry
Full Definition of 
spinster:     
1:  a woman whose occupation is to spin 
2 a:  archaic   :  an unmarried woman of gentle family 
   b:  an unmarried woman and especially one past the common age for marrying 
3:  a woman who seems unlikely to marry
3. My answer to my niece when she asks me when I am going to get a boyfriend.  Also, my answer to my nephew-in-law when he says that I need to get a boyfriend.