Limerence is regularly tied with the term “crushing on someone”, but this relation is wrong. Regardless of whether those feelings are returned or not, to crush on someone means that you have developed feelings of desire for a person. Limerence is where one desires someone and that desire is fueled by reciprocation from the person they desire.
Whereas a crush on someone or puppy love can last for merely days or weeks. Limerence has been known to last for at least several months or even years.
A crush is usually consciously formed, while limerence is usually an unwanted cerebral state of mind that forms on the subconscious level. Someone demonstrating the effects of limerence would practically walk on water if they came in contact with the person of their desire. While a simple crush would cause more subdued actions. The website, Lovepanky, voices their opinion on the matter, here.
Strangely, during certain periods, one with limerence may not display any emotion or feeling toward the person they crave. These are considered low lying periods. Conversely, low lying periods are replaced with hope for reciprocation; as well as enormous amounts of energy that are devoted to obsession.
Interestingly, there doesn’t appear to be much recorded history on the etymology (or origins) of the word limerence. It appears that the word was adapted initially from word, limerent. The second definition of limerent meant 'learned in skulls'. This was only used once in 1819 in a phrenological (this simply refers to the science of measuring a human skull) context.
In 1977, The Observer published the following by Dorothy Tennov: “I first used the term ‘amorance’ then changed it back to ‘limerence’... It has no roots whatsoever. It looks nice. It works well in French. Take it from me, it has no etymology whatsoever.” To learn more about this fascinating word, go here.