In the user's guide for the
amsmath package (Version 2.1) on page 3, the descriptions for the options
fleqn are as follows:
leqno: Place equation numbers on the left.
fleqn: Position equations at a fixed indent from the left margin rather than centered in the text column.
However, the meaning of the abbreviations "leqno" and "fleqn" are not immediately clear from these descriptions. In a response on this link, the following meanings were suggested:
leqno: left equation numbers
fleqn: flush left equations
According to Merriam-Webster Dictionary's entry for "no," which states that it is derived from the Latin word "numero" (ablative of "numerus"), it can be understood as meaning "number."
Therefore, it can be inferred that
leqno stands for "left equation no". However, it is unclear what the "n" in
fleqn stands for if it is interpreted as "flush left equations."
I was not able to find a definitive explanation for the abbreviations
fleqn and their corresponding words through a search engine. It seems that the suggested meanings are based on reasonable deductions/guesses.
PS: English is not my native language, so please forgive any typos or inaccuracies in my expression. If there is any unclear part of my question, please let me know, and I will be happy to rephrase it until we can communicate effectively. Similarly, I am willing to do what I can to help in the process of finding an answer.