Note - this question was inspired by this questions on physics.SE.
Many (most) physical quantities are denoted with a single letter - latin or greek. For many, the letter chosen makes sense: $t$ for time, $m$ for mass, etc. Often the letter chosen either relates to the word for the quantity (in the language of the person first describing it, or Latin or Greek) or indeed the name of the discoverer. Occasionally, the letter is borrowed from another field with a similar use. For example, the letter $n$ is often used for counting natural numbers, and thus became associated with quantum numbers.
All of which leaves me to wonder: why did angular momentum get the letter $L$? I saw a few "answers" online that I found very unsatisfactory - that it related to "Left", or the right angle made between the velocity and position vectors... I suspect there is a deeper explanation but it has eluded me. I tried looking at some of the early descriptions by Newton, Hooke and Kepler but didn't find an answer.